drm/amdgpu/pm: add EnableGfxImu message dummy map for SMU IP v13.0.4

The SMU needs this message to trigger IMU initialization.

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