ORIGEN: Enhance origen config to be more flexible on boot.

This patch enhances the boot of origen board by adding support to ext2, bootz, initrd, bootenv loading and boot script.
It still keeps the previous mmc load command if boot script fails.

Signed-off-by: Guillaume GARDET <guillaume.gardet@free.fr>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>