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>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index f641bb0..ee58cde 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -68,7 +68,7 @@
 
 ######
 # gcc support functions
-# See documentation in Documentation/kbuild/makefiles.txt
+# See documentation in Documentation/kbuild/makefiles.rst
 
 # cc-cross-prefix
 # Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu- m68k-linux-)
@@ -210,7 +210,7 @@
 # if_changed_dep  - as if_changed, but uses fixdep to reveal dependencies
 #                   including used config symbols
 # if_changed_rule - as if_changed but execute rule instead
-# See Documentation/kbuild/makefiles.txt for more info
+# See Documentation/kbuild/makefiles.rst for more info
 
 ifneq ($(KBUILD_NOCMDDEP),1)
 # Check if both arguments are the same including their order. Result is empty