hw/arm/vexpress: Don't set info->secure_boot if CPU doesn't have EL3

hw/arm/vexpress: Don't set info->secure_boot if CPU doesn't have EL3

Don't request that the arm_load_kernel() code should boot in secure
state if the CPU doesn't have a secure state. Currently this
doesn't make a difference because the boot.c code only examines
the secure_boot flag in code guarded by an ARM_FEATURE_EL3 check,
but upcoming changes for supporting booting into Hyp mode will
change that.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Message-id: 20180821132811.17675-9-peter.maydell@linaro.org