We don't need to use the PCI BAR on APUs. This allows us to access
the full VRAM directly without being limited by the BAR size.

v2: squash in 64bit shift fix
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NMichel Dänzer <michel.daenzer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>