uboot-imx

configs: k2x_evm: Adds environment variables for secure devices

Updates the default u-boot environment variables to support secure
boot. On secure devices, a secure boot monitor (sec-bm) needs to
be installed by u-boot.

Signed-off-by: Madan Srinivas <madans@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>