drm/amdgpu/powerplay: declare firmware for CI cards

Missing firmware declaration caused firmware requirement to
not be noted by the module and may cause firmware to not
be available in initrd.

Fixes: bc4b539e "drm/amdgpu: remove old CI DPM implementation"
Reviewed-by: James Zhu <James.Zhu@amd.com>
Tested-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>