drm/amdgpu/discovery: handle AMDGPU_FW_LOAD_RLC_BACKDOOR_AUTO in SMU

Handle SMU load ordering when firmware load type is
AMDGPU_FW_LOAD_RLC_BACKDOOR_AUTO.  This works similarly
to AMDGPU_FW_LOAD_DIRECT where the SMU load order is
different from the standard ordering when front door
loading is enabled.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>