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>

WHENCE

@@ -2289,6 +2289,7 @@ File: amdgpu/polaris12_ce.bin
 File: amdgpu/polaris12_ce_2.bin
 File: amdgpu/polaris12_mc.bin
 File: amdgpu/polaris12_k_mc.bin
+File: amdgpu/polaris12_32_mc.bin
 File: amdgpu/polaris12_me.bin
 File: amdgpu/polaris12_me_2.bin
 File: amdgpu/polaris12_mec.bin