drm/amdgpu: log when amdgpu.dc=1 but ASIC is unsupported

This makes it easier to figure out whether the kernel parameter has been
taken into account.

Signed-off-by: Simon Ser <[e-mail]>
Cc: Harry Wentland <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

···
 		return amdgpu_dc != 0;
 #endif
 	default:
+		if (amdgpu_dc > 0)
+			DRM_INFO("Display Core has been requested via kernel parameter "
+					 "but isn't supported by ASIC, ignoring\n");
 		return false;
 	}
 }