smumgr provides the interface for interacting with the
smu firmware which handles power management.

v2: squash in updates (Alex)
Signed-off-by: NRex Zhu <Rex.Zhu@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: NHawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>