drm/amdgpu: enable imu firmware for GC 11.0.4

The GC 11.0.4 needs load IMU to power up GFX before loads GFX firmware.

Signed-off-by: Li Ma <li.ma@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>