Switch U-Boot from vendor downstream version to upstream. Since the
upstream U-Boot uses binman to build the bootable binary (flash.bin) the
need for the iMX specifc prepare script is no longer required.
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>