Powerplay will use them instead of raw printk, and we can dynamic
change the debug level with it.

The prefix is like below:

[  xxx.xxxxxx] amdgpu: [powerplay] ...
Suggested-by: NGrazvydas Ignotas <notasas@gmail.com>
Signed-off-by: NHuang Rui <ray.huang@amd.com>
Cc: Arindam Nath <Arindam.Nath@amd.com>
Reviewed-by: NEdward O'Callaghan <funfunctor@folklore1984.net>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>