DRM: Armada: depend on ARM

Armada DRM uses relaxed accessors which are not available on other
platforms.  Limit it to just ARM.
Acked-by: NRob Clark <robdclark@gmail.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

drivers/gpu/drm/armada/Kconfig

 config DRM_ARMADA
 	tristate "DRM support for Marvell Armada SoCs"
-	depends on DRM && HAVE_CLK
+	depends on DRM && HAVE_CLK && ARM
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT