drm: atmel-hlcdc: Add dependency on ARM

The atmel-hlcdc driver selects DRM_GEM_CMA_HELPER which makes use of
symbols only available when HAVE_DMA_ATTRS is selected.
Add a dependency on the ARM architecture which select this option.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Dave Airlie <airlied@gmail.com>

drivers/gpu/drm/atmel-hlcdc/Kconfig

 config DRM_ATMEL_HLCDC
 	tristate "DRM Support for ATMEL HLCDC Display Controller"
-	depends on DRM && OF && COMMON_CLK && MFD_ATMEL_HLCDC
+	depends on DRM && OF && COMMON_CLK && MFD_ATMEL_HLCDC && ARM
 	select DRM_GEM_CMA_HELPER
 	select DRM_KMS_HELPER
 	select DRM_KMS_FB_HELPER