drm/amdgpu: introduce two work mode for imu

IMU has two work mode such as debug mode and mission mode. Current GC
v11_0_0 is using the debug mode.

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