docs: kbuild: convert docs to ReST and rename to *.rst

The kbuild documentation clearly shows that the documents
there are written at different times: some use markdown,
some use their own peculiar logic to split sections.

Convert everything to ReST without affecting too much
the author's style and avoiding adding uneeded markups.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/kconfig/tests/err_recursive_dep/expected_stderr

@@ -1,38 +1,38 @@
 Kconfig:11:error: recursive dependency detected!
 Kconfig:11:	symbol B is selected by B
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:5:error: recursive dependency detected!
 Kconfig:5:	symbol A depends on A
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:17:error: recursive dependency detected!
 Kconfig:17:	symbol C1 depends on C2
 Kconfig:21:	symbol C2 depends on C1
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:32:error: recursive dependency detected!
 Kconfig:32:	symbol D2 is selected by D1
 Kconfig:27:	symbol D1 depends on D2
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:37:error: recursive dependency detected!
 Kconfig:37:	symbol E1 depends on E2
 Kconfig:42:	symbol E2 is implied by E1
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:60:error: recursive dependency detected!
 Kconfig:60:	symbol G depends on G
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
 
 Kconfig:51:error: recursive dependency detected!
 Kconfig:51:	symbol F2 depends on F1
 Kconfig:49:	symbol F1 default value contains F2
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"