arm: sam9_l9260_defconfig: prepare to UBI config change
We are going to kill the CONFIG_MTD_UBI_BEB_RESERVE configuration option soon
and use the CONFIG_MTD_UBI_BEB_LIMIT instead. In order to do this smoothly,
we now introduce the new configuration option to sam9_l9260_defconfig, and
will kill the old one after the corresponding UBI changes are done.