drm/amdgpu: Allocate psp fw private buffer in vram

It's not necessarily to allocate psp firmware private
buffer in different memory domain in sriov and bare
metal environment

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>