amdgpu: add vega20 TA firmware from 20.20 release

Based on internal commit:
c6aa2bdaa30af815fc257f2b0e50f6c66d74045c
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -2304,6 +2304,7 @@ File: amdgpu/vega20_smc.bin
 File: amdgpu/vega20_sos.bin
 File: amdgpu/vega20_uvd.bin
 File: amdgpu/vega20_vce.bin
+File: amdgpu/vega20_ta.bin
 File: amdgpu/raven_asd.bin
 File: amdgpu/raven_ce.bin
 File: amdgpu/raven_gpu_info.bin