Spawning AArch64 VMs using salt.control.virt requires a few extra
domain configuration items to be configurable:
- libvirt xml: pass loader param to vm
  Based on upstream commit [1].
- libvirt xml: pass virt machine type
- libvirt xml: pass cpu mode to vm
- virt module: Allow NVRAM unlinking on DOM undefine
  UEFI-enabled VMs usually have pflash (NVRAM) devices attached,
  which require one additional libvirt flag to be passed at 'undefine'.
  This is usually the case for AArch64 (arm64) VMs, where AAVMF (AA64
  UEFI) is the only supported guest bootloader.

[1] https://github.com/saltstack/salt/commit/9cace9adb

Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>