drm/amdgpu: support polaris10/11/12 new cp firmwares

Newer versions of the CP firmware require changes in how the driver
initializes the hw block.
Change the firmware name for new firmware to maintain compatibility with
older kernels.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>