drm/amdgpu: register pm sysfs for sriov (v2)

we need register pm sysfs for virt in order
to support dpm level modification because
smu ip block will not be added under SRIOV

v2: whitespace fixes (Alex)

Signed-off-by: Yintian Tao <yttao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>