warp7: defconfig: Enable OPTEE for WaRP7

Requires setting CONFIG_OPTEE=y and setting an OPTEE TrustZone DRAM base in
include/configs/warp7.h.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>