drm/amdgpu/sriov: Add clear vf fw support

Guest VM issue the PSP clear_vf_fw command at 2 points:
1.On VF driver loading, after VF message PSP to setup rings,
the next command is “clear_vf_fw”
2.On VF driver unload before VF message to
destroy rings

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Ack-by: Monk.liu <monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>