ARM: mxs_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.

Note that this does not remove CONFIG_FB. CONFIG_FB gets selected
implicity by CONFIG_DRM/CONFIG_DRM_KMS_FB_HELPER.
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/configs/mxs_defconfig

@@ -94,8 +94,9 @@ CONFIG_STMP3XXX_RTC_WATCHDOG=y
 CONFIG_MFD_MXS_LRADC=y
 CONFIG_REGULATOR=y
 CONFIG_REGULATOR_FIXED_VOLTAGE=y
-CONFIG_FB=y
-CONFIG_FB_MXS=y
+CONFIG_DRM=y
+CONFIG_DRM_MXSFB=y
+CONFIG_FB_MODE_HELPERS=y
 CONFIG_BACKLIGHT_LCD_SUPPORT=y
 CONFIG_LCD_CLASS_DEVICE=y
 CONFIG_BACKLIGHT_CLASS_DEVICE=y