gma500: kill virtual mapping support

This isn't actually usable - we simply don't have the vmap space on a 32bit
system to do this stunt. Instead we will rely on the low level drivers
limiting the console resolution as before.

The real fix is for someone to write a page table aware version of the
framebuffer console blit functions. Good university student project
perhaps..

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>