Revert "ARM: imx_v6_v7_defconfig: use MXSFB DRM driver"

This reverts commit aaeabc18.

Since, on legacy i.MX6 and i.MX7 series, only framebuffer driver
can be supported.

Signed-off-by: Fancy Fang <chen.fang@nxp.com>

arch/arm/configs/imx_v6_v7_defconfig

@@ -310,8 +310,7 @@ CONFIG_DRM_IMX_TVE=y
 CONFIG_DRM_IMX_LDB=y
 CONFIG_DRM_IMX_HDMI=y
 CONFIG_DRM_ETNAVIV=y
-CONFIG_DRM_MXSFB=y
-CONFIG_FB_MODE_HELPERS=y
+CONFIG_FB_MXS=y
 CONFIG_LCD_CLASS_DEVICE=y
 CONFIG_LCD_L4F00242T03=y
 CONFIG_LCD_PLATFORM=y