Add a flag to build husky with nvhe hypervisor

Android Virtualization Framework (AVF) team is planning to use husky as
a development platform while working on the infrastructure to support
assigning devices to guest VMs. In order to test the kernel/user space
code we will need to run hypervisor in nvhe mode.

Bug: 278008256
Test: flash build and check that hypervisor is in nvhe mode
Change-Id: Ide100f571813e9b8a1eba7b57f050d2f7093cd86