drm/amd/powerplay: add and export hwmgr interface to eventmgr to check hw states.

Interface between hwmgr and eventmgr.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>