drm/amd/powerplay: refine smumgr code

1. delete asic_smum_init functions, export asic private functions
   to smumgr directly, make code more readable.
2. create asic private data in asic_init_func.

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