drm/amdgpu: add ucode_start_address into cgs_firmware_info

The ucode_start_address would be used on powerplay of iceland.

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