drm/amd/pp: Use gfx rlc funcs directly in powerplay

In order to remove cgs interfaces:
cgs_enter_safe_mode
cgs_lock_grbm_idx

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>