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

Convert kdump documentation to ReST and add it to the
user faced manual, as the documents are mainly focused on
sysadmins that would be enabling kdump.

Note: the vmcoreinfo.rst has one very long title on one of its
sub-sections:

	PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision|PG_head_mask|PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)

I opted to break this one, into two entries with the same content,
in order to make it easier to display after being parsed in html and PDF.

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>

Documentation/powerpc/firmware-assisted-dump.txt

@@ -59,7 +59,7 @@ as follows:
          the default calculated size. Use this option if default
          boot memory size is not sufficient for second kernel to
          boot successfully. For syntax of crashkernel= parameter,
-         refer to Documentation/kdump/kdump.txt. If any offset is
+         refer to Documentation/kdump/kdump.rst. If any offset is
          provided in crashkernel= parameter, it will be ignored
          as fadump uses a predefined offset to reserve memory
          for boot memory dump preservation in case of a crash.