docs: fb: Remove matroxfb scrollback boot option

In commit 50145474f6ef ("fbcon: remove soft scrollback code"), the
framebuffer scrollback mode was removed, but the documentation was not
updated. Properly update the documentation by removing the option that
is no longer pressent, and removed the particular scrollback option.

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/e5187e70faf8237825a142313802983a6c214baa.1600333774.git.unixbhaskar@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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

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.

Also, removed the Maintained by, as requested by Geert.

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