pico-imx7d: Enable CONFIG_ARMV7_BOOT_SEC_DEFAULT

pico-imx7d: Enable CONFIG_ARMV7_BOOT_SEC_DEFAULT

Currently the CAAM driver fails to be probed:

caam 30900000.caam: Entropy delay = 3200
caam 30900000.caam: failed to acquire DECO 0
caam 30900000.caam: failed to instantiate RNG

CAAM needs to be initialized in secure world, so enable
CONFIG_ARMV7_BOOT_SEC_DEFAULT to allow the driver to
probe successfully.

Tested with kernel mainline version 4.17.2.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>