amdgpu: add raven dmcu firmware

This adds the display management controller firmware for
raven.

From internal git commit:
a22dd4994b810a141ba3cdc608d37eda8a206c1a
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -2164,6 +2164,7 @@ File: amdgpu/raven_pfp.bin
 File: amdgpu/raven_rlc.bin
 File: amdgpu/raven_sdma.bin
 File: amdgpu/raven_vcn.bin
+File: amdgpu/raven_dmcu.bin
 
 Licence: Redistributable. See LICENSE.amdgpu for details.