drm/radeon/kms: MC vram map needs to be >= pci aperture size

drm/radeon/kms: MC vram map needs to be >= pci aperture size

commit b7d8cce5b558e0c0aa6898c9865356481598b46d upstream.

The vram map in the radeon memory controller needs to be
>= the pci aperture size.  Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=28402

The problematic cards in the above bug have 64 MB of vram,
but the pci aperture is 128 MB and the MC vram map was only
64 MB.  This can lead to hangs.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>