drm/amdgpu/display: fix warning when CONFIG_DRM_AMD_DC_DCN is not set

dm_dcn_crtc_high_irq() is only used when CONFIG_DRM_AMD_DC_DCN is set.
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -485,7 +485,7 @@ static void dm_crtc_high_irq(void *interrupt_params)
 	}
 }
 
-
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 /**
  * dm_dcn_crtc_high_irq() - Handles VStartup interrupt for DCN generation ASICs
  * @interrupt params - interrupt parameters
@@ -547,6 +547,7 @@ static void dm_dcn_crtc_high_irq(void *interrupt_params)
 
 	spin_unlock_irqrestore(&adev->ddev->event_lock, flags);
 }
+#endif
 
 static int dm_set_clockgating_state(void *handle,
 		  enum amd_clockgating_state state)