drm/amdgpu: bypass FB resizing for SRIOV VF

It introduces 900ms latency in exclusive mode which causes failure
of driver loading. Host can resize the BAR before guest staring,
so the resizing is not necessary here.

Signed-off-by: Pixel Ding <Pixel.Ding@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>