Use a command line option (vram) rather than hardcoding the vram size.  LxFB
already does this; it's useful for machines that can't query the BIOS for fb
size.  This patch originated from David Woodhouse, was modified by Jordan
Crouse, and was then modified further by me.

This also adds some gxfb documentation in Documentation/fb.
Signed-off-by: NAndres Salomon <dilinger@debian.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>