The amdgu_powerplay variable is global for multiple GPU instances.

v2: fold in Flora's module option change, protect adev reference in
macros
Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>