linux-next: build failure after merge of the amdgpu tree

Hi all,

After merging the amdgpu tree, today's linux-next build (x86_64
allmodconfig) failed like this:

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c: In function 'dm_set_vblank':
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:5493:2: error: implicit declaration of function 'dc_allow_idle_optimizations' [-Werror=implicit-function-declaration]
 5493 |  dc_allow_idle_optimizations(
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Caused by commit

  71338cb4a7c2 ("drm/amd/display: enable idle optimizations for linux (MALL stutter)")

I have used the amdgpu tree from next-20210107 for today.
dc_allow_idle_optimizations() is only declared when CONFIG_DRM_AMD_DC_DCN
is set.

-- 
Cheers,
Stephen Rothwell