drm/amd/display/amdgpu_dm/amdgpu_dm_helpers: Move defines out to where they are actually used

Fixes the following W=1 kernel build warning(s):

  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h: At top level:
  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h:143:22:
      warning: ‘SYNAPTICS_DEVICE_ID’ defined but not used [-Wunused-const-variable=]
  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h:140:22:
      warning: ‘DP_VGA_LVDS_CONVERTER_ID_3’ defined but not used [-Wunused-const-variable=]
  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h:138:22:
      warning: ‘DP_VGA_LVDS_CONVERTER_ID_2’ defined but not used [-Wunused-const-variable=]
  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h:133:22:
      warning: ‘DP_SINK_DEVICE_STR_ID_2’ defined but not used [-Wunused-const-variable=]
  drivers/gpu/drm/amd/amdgpu/../display/include/ddc_service_types.h:132:22:
      warning: ‘DP_SINK_DEVICE_STR_ID_1’ defined but not used [-Wunused-const-variable=]

[snip 400 similar lines brevity]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>