drm/amdgpu: Set PG state to gating for vcn_v_5_0_1

For vcn_v_5_0_1, set power state to gating during hw fini. Also there may
be scenario where VCN engine hangs during a job execution, then it's not
safe to assume that set_pg_state works fine during hw_fini to put the state
to gated. After a reset, we can assume that it's in the default state,
therefore reset the driver maintained state. Put the default state as gated
during reset as per this assumption.

Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>