drm/exynos: add support for ARCH_MULTIPLATFORM

Exynos does not seem to have any dependency on anything from
platform headers so just needs Kconfig updated to build in
ARCH_MULTIPLATFORM builds.
Signed-off-by: NRob Clark <rob@ti.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/Kconfig

 config DRM_EXYNOS
 	tristate "DRM Support for Samsung SoC EXYNOS Series"
-	depends on DRM && PLAT_SAMSUNG
+	depends on DRM && (PLAT_SAMSUNG || ARCH_MULTIPLATFORM)
 	select DRM_KMS_HELPER
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA