hw/arm/boot: AArch32 kernels should be started in Hyp mode if available

hw/arm/boot: AArch32 kernels should be started in Hyp mode if available

The kernel booting specification for an AArch32 kernel requires that
it is booted in Hyp mode if available; otherwise the kernel can't
enable KVM. We were incorrectly leaving the kernel in SVC mode.
If we're booting an AArch32 kernel in the Nonsecure state and Hyp
mode is available, start in it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Message-id: 20180820153020.21478-7-peter.maydell@linaro.org