drm/amd/display: Refine the implementation of dm_pp_get_funcs_rv

powerplay/dpm export all interfaces in struct amd_pm_funcs.
so call common exported interfaces instead of powerplay inner interfaces

Also not include header file hwmgr.h

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