doc: Replace DocBook with sphinx-based docs

The Linux kernel moved to sphinx-based documentation and got rid of the
DocBook based documentation quite a while ago. Hence, the DocBook
documentation for U-Boot should be converted as well.

To achieve this, import the necessary files from Linux v4.17, and
convert the current DocBook documentation (three files altogether) to
sphinx/reStructuredText.

For now, all old DocBook documentation was merged into a single
handbook, tentatively named "U-Boot Hacker Manual".

For some source files, the documentation style was changed to comply
with kernel-doc; no functional changes were applied.

Signed-off-by: Mario Six <mario.six@gdsys.cc>

1 files changed, 117 insertions, 0 deletions

diff --git a/Documentation/index.rst b/Documentation/index.rst
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+====================
+U-Boot Hacker Manual
+====================
+
+Linker-Generated Arrays
+=======================
+
+A linker list is constructed by grouping together linker input
+sections, each containing one entry of the list. Each input section
+contains a constant initialized variable which holds the entry's
+content. Linker list input sections are constructed from the list
+and entry names, plus a prefix which allows grouping all lists
+together. Assuming _list and _entry are the list and entry names,
+then the corresponding input section name is
+
+::
+
+  .u_boot_list_ + 2_ + @_list + _2_ + @_entry
+
+and the C variable name is
+
+::
+
+  _u_boot_list + _2_ + @_list + _2_ + @_entry
+
+This ensures uniqueness for both input section and C variable name.
+
+Note that the names differ only in the first character, "." for the
+section and "_" for the variable, so that the linker cannot confuse
+section and symbol names. From now on, both names will be referred
+to as
+
+::
+
+  %u_boot_list_ + 2_ + @_list + _2_ + @_entry
+
+Entry variables need never be referred to directly.
+
+The naming scheme for input sections allows grouping all linker lists
+into a single linker output section and grouping all entries for a
+single list.
+
+Note the two '_2_' constant components in the names: their presence
+allows putting a start and end symbols around a list, by mapping
+these symbols to sections names with components "1" (before) and
+"3" (after) instead of "2" (within).
+Start and end symbols for a list can generally be defined as
+
+::
+
+  %u_boot_list_2_ + @_list + _1_...
+  %u_boot_list_2_ + @_list + _3_...
+
+Start and end symbols for the whole of the linker lists area can be
+defined as
+
+::
+
+  %u_boot_list_1_...
+  %u_boot_list_3_...
+
+Here is an example of the sorted sections which result from a list
+"array" made up of three entries : "first", "second" and "third",
+iterated at least once.
+
+::
+
+  .u_boot_list_2_array_1
+  .u_boot_list_2_array_2_first
+  .u_boot_list_2_array_2_second
+  .u_boot_list_2_array_2_third
+  .u_boot_list_2_array_3
+
+If lists must be divided into sublists (e.g. for iterating only on
+part of a list), one can simply give the list a name of the form
+'outer_2_inner', where 'outer' is the global list name and 'inner'
+is the sub-list name. Iterators for the whole list should use the
+global list name ("outer"); iterators for only a sub-list should use
+the full sub-list name ("outer_2_inner").
+
+Here is an example of the sections generated from a global list
+named "drivers", two sub-lists named "i2c" and "pci", and iterators
+defined for the whole list and each sub-list:
+
+::
+
+  %u_boot_list_2_drivers_1
+  %u_boot_list_2_drivers_2_i2c_1
+  %u_boot_list_2_drivers_2_i2c_2_first
+  %u_boot_list_2_drivers_2_i2c_2_first
+  %u_boot_list_2_drivers_2_i2c_2_second
+  %u_boot_list_2_drivers_2_i2c_2_third
+  %u_boot_list_2_drivers_2_i2c_3
+  %u_boot_list_2_drivers_2_pci_1
+  %u_boot_list_2_drivers_2_pci_2_first
+  %u_boot_list_2_drivers_2_pci_2_second
+  %u_boot_list_2_drivers_2_pci_2_third
+  %u_boot_list_2_drivers_2_pci_3
+  %u_boot_list_2_drivers_3
+
+.. kernel-doc:: include/linker_lists.h
+   :internal:
+
+Serial system
+=============
+
+.. kernel-doc:: drivers/serial/serial.c
+   :internal:
+
+The U-Boot EFI subsystem
+========================
+
+Boot services
+-------------
+
+.. kernel-doc:: lib/efi_loader/efi_boottime.c
+   :internal: