drm/amdgpu: Refine function name and function args

There are no any logical changes here.

1. change function names:
   amdgpu_device_ip_late_set_pg/cg_state to
   amdgpu_device_set_pg/cg_state.
2. add a function argument cg/pg_state, so
   we can enable/disable cg/pg through those functions

Reviewed-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>