ARM: imx_v6_v7_defconfig: use MXSFB DRM driver

Use the the DRM driver for MXSFB LCD controller (used in i.MX23/
i.MX28/i.MX6SX or i.MX7). Remove CONFIG_FB_MXS which will soon be
removed.
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -266,7 +266,8 @@ CONFIG_DRM_IMX_TVE=y
 CONFIG_DRM_IMX_LDB=y
 CONFIG_DRM_IMX_HDMI=y
 CONFIG_DRM_ETNAVIV=y
-CONFIG_FB_MXS=y
+CONFIG_DRM_MXSFB=y
+CONFIG_FB_MODE_HELPERS=y
 CONFIG_LCD_CLASS_DEVICE=y
 CONFIG_LCD_L4F00242T03=y
 CONFIG_LCD_PLATFORM=y