Due to lack of MODULE_FIRMWARE() with hainan_mc.bin, the driver
doesn't work properly in initrd.  Let's add it.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1116239
Fixes: 8eaf2b1f ("drm/amdgpu: switch firmware path for SI parts")
Cc: <stable@vger.kernel.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>