imx6: add wandboard management in u-boot build.

Add Wandboard dl and quad configuration and add patch to improve u-boot for wandboard.

Signed-off-by: XoD <xoddark@gmail.com>
imx6: add wandboard uboot management in create_sdcard

Signed-off-by: XoD <xoddark@gmail.com>
imx6: fix u-boot bootloader file test.

Fix test of present file for bootloader to install.

Signed-off-by: XoD <xoddark@gmail.com>