drm/amdgpu/gmc8: always load MC firmware in the driver

Some power features rely on the driver loaded version so always
load the MC firmware from the driver even if the vbios loaded
a version already.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org