amdgpu: add firmware for vega20 from 18.50

From internal git commit:
534e4d6a23b55c75a4b60ebdb323118ee1f4e08d
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -2180,6 +2180,19 @@ File: amdgpu/vega12_smc.bin
 File: amdgpu/vega12_sos.bin
 File: amdgpu/vega12_uvd.bin
 File: amdgpu/vega12_vce.bin
+File: amdgpu/vega20_asd.bin
+File: amdgpu/vega20_ce.bin
+File: amdgpu/vega20_me.bin
+File: amdgpu/vega20_mec.bin
+File: amdgpu/vega20_mec2.bin
+File: amdgpu/vega20_pfp.bin
+File: amdgpu/vega20_rlc.bin
+File: amdgpu/vega20_sdma.bin
+File: amdgpu/vega20_sdma1.bin
+File: amdgpu/vega20_smc.bin
+File: amdgpu/vega20_sos.bin
+File: amdgpu/vega20_uvd.bin
+File: amdgpu/vega20_vce.bin
 File: amdgpu/raven_asd.bin
 File: amdgpu/raven_ce.bin
 File: amdgpu/raven_gpu_info.bin