drm/amd/pm: introduce a new set of OD interfaces

There will be multiple interfaces(sysfs files) exposed with each representing
a single OD functionality. And all those interface will be arranged in a tree
liked hierarchy with the top dir as "gpu_od". Meanwhile all functionalities
for the same component will be arranged under the same directory.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>