arm: imx_v6_v7_defconfig: enable FB_MXC_OVERLAY config

Enable FB_MXC_OVERLAY config by default for the lcdif
driver on legacy i.MX6 and i.MX7 platforms.

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

arch/arm/configs/imx_v6_v7_defconfig

@@ -335,6 +335,7 @@ CONFIG_FB_MXC_TRULY_PANEL_TFT3P5581E=y
 CONFIG_FB_MXC_RK_PANEL_RK055AHD042=y
 CONFIG_FB_MXC_RK_PANEL_RK055IQH042=y
 CONFIG_FB_MXC_SYNC_PANEL=y
+CONFIG_FB_MXC_OVERLAY=y
 CONFIG_FB_MXC_LDB=y
 CONFIG_FB_MXC_HDMI=y
 CONFIG_FB_MXS_SII902X=y