[TESTS] Make Virt-v8 guest consistent with other hypervisors

There has been on-going effort in linaro to standardize the
VM/Guest HW for KVM and Xen. As part of these effort, the
QEMU mach-virt machine model will implement this standardized
VM/Guest HW for KVM. Linaro is also putting efforts to provide
UEFI firmware for standardized VM/Guest HW.

To get the benifits of this standardized VM/Guest HW we make
Virt-v8 machine mode compatible with QEMU mach-virt machine
model. In future, we would be also having Virt-v7 machine
model similar to Virt-v8 machine model for arm32ve.

Signed-off-by: Anup Patel <anup@brainfault.org>