drm/amdgpu/gfx10: declare cp/rlc firmwares for navi12

Set the name properly to load the right ucode.

Signed-off-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>