drm/amdgpu: enable imu firmware for GC 11.0.1

The GC 11.0.1 needs load IMU to power up the GFX before loads GFX
firmware.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>