amdgpu: add new polaris 12 MC firmware

New firmware for polaris12 boards with a 32bit MC config.

From internal git commit:
c0f66ec7ae6a410b3607579401a6565fefbf18ed

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>