fbdev: simplefb: add common x86 RGB formats

32bit XRGB and ARGB are used by modern x86 systems for EFI and VESA
framebuffers. The other formats were reported by hpa to be most common.
Add these so simplefb works on most common x86 systems.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Link: http://lkml.kernel.org/r/1375445127-15480-6-git-send-email-dh.herrmann@gmail.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>