amdgpu: add firmware for VCN 3.1.2 IP block

From internal git commit:
33d6b5ddb01bba420792f2c89882d678c991aacd

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -2540,6 +2540,7 @@ File: amdgpu/psp_13_0_8_ta.bin
 File: amdgpu/psp_13_0_8_toc.bin
 File: amdgpu/sdma_5_2_6.bin
 File: amdgpu/sdma_5_2_7.bin
+File: amdgpu/vcn_3_1_2.bin
 
 Licence: Redistributable. See LICENSE.amdgpu for details.