uboot-imx

imx: mx6ulevk: change mtest memory size to 128M

To i.MX6UL 14x14 EVK, system memory is 512M; to i.MX6UL 9x9 EVK,
system memory is 256M. If setting mtest size to 256M, mtest will
crash uboot for i.MX6UL 9x9 evk. So change mtest size to 128M.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>