gxfb: replace FBSIZE config option with a module parameter

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: Andres Salomon <dilinger@debian.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/fb/gxfb.txt

@@ -0,0 +1,51 @@
+[This file is cloned from VesaFB/aty128fb]
+
+What is gxfb?
+=================
+
+This is a graphics framebuffer driver for AMD Geode GX2 based processors.
+
+Advantages:
+
+ * No need to use AMD's VSA code (or other VESA emulation layer) in the
+   BIOS.
+ * It provides a nice large console (128 cols + 48 lines with 1024x768)
+   without using tiny, unreadable fonts.
+ * You can run XF68_FBDev on top of /dev/fb0
+ * Most important: boot logo :-)
+
+Disadvantages:
+
+ * graphic mode is slower than text mode...
+
+
+How to use it?
+==============
+
+Switching modes is done using  gxfb.mode_option=<resolution>... boot
+parameter or using `fbset' program.
+
+See Documentation/fb/modedb.txt for more information on modedb
+resolutions.
+
+
+X11
+===
+
+XF68_FBDev should generally work fine, but it is non-accelerated.
+
+
+Configuration
+=============
+
+You can pass kernel command line options to gxfb with gxfb.<option>.
+For example, gxfb.mode_option=800x600@75.
+Accepted options:
+
+mode_option	- specify the video mode.  Of the form
+		  <x>x<y>[-<bpp>][@<refresh>]
+vram		- size of video ram (normally auto-detected)
+
+
+--
+Andres Salomon <dilinger@debian.org>