at91: Add ext4 filesystem

Add ext4 filesystem for creating sdcard image with ext4 rootfs and
removing ext2 as it superset of ext4.

Signed-off-by: Sandeep Sheriker Mallikarjun <[email protected]>

target/linux/at91/Makefile

@@ -10,7 +10,7 @@ ARCH:=arm
 BOARD:=at91
 MAINTAINER:=Claudio Mignanti <[email protected]>
 BOARDNAME:=Microchip (Atmel AT91)
-FEATURES:=squashfs targz ext2 usb usbgadget ubifs
+FEATURES:=ext4 squashfs targz usb usbgadget ubifs
 SUBTARGETS:=sama5 legacy
 
 KERNEL_PATCHVER:=4.4