drm/amdgpu: remove sriov vf gfxhub fb location programming

host driver programmed the gfxhub fb location for vf, no need to
program in guest side.

Signed-off-by: Zhigang Luo <zhigang.luo@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-By : Shaoyun.liu <shaoyunl@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>