warp7: defconfig: Enable CONFIG_SECURE_BOOT

Various function associated with booting the WaRP7 in High Assurance Boot
(HAB) mode are enabled by switching on CONFIG_SECURE_BOOT.

This patch enables CONFIG_SECURE_BOOT for the WaRP7 defconfig.
Signed-off-by: NBryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: NBreno Lima <breno.lima@nxp.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>

configs/warp7_defconfig

 CONFIG_ARM=y
 CONFIG_ARCH_MX7=y
+CONFIG_SECURE_BOOT=y
 CONFIG_SYS_TEXT_BASE=0x87800000
 CONFIG_TARGET_WARP7=y
 # CONFIG_ARMV7_VIRT is not set