fix radeonfb regression with Xpress 200m 5955

Fix http://bugzilla.kernel.org/show_bug.cgi?id=9762

Framebuffer is ok only with default parameters only (it is 1280x800-8@60).  If
parameters are video=radeonfb:1280x800-32@60 then xres, yres and xres_virtual
are ok but yres_virtual is 1024.  It can be corrected by fbset utility so I
think it can be corrected in the driver code also.

Steps to reproduce: video=radeonfb:1280x800-32@60 or
video=radeonfb:1280x800-16@60

Add 1280x800 mode into modedb

Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>