drm/amdgpu: put SMU into proper state on runpm suspending for BOCO capable platform

By setting mp1_state as PP_MP1_STATE_UNLOAD, MP1 will do some proper cleanups and
put itself into a state ready for PNP. That can workaround some random resuming
failure observed on BOCO capable platforms.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>