salt: virt: Extend libvirt_domain

salt: virt: Extend libvirt_domain

Extend salt virt modelling capabilities with support for:
- hw_firmware_type;
- virt_machine_model;
- cpu_model;

This requires extending/patching:
- libvirt_domain.jinja template (part of salt package, handled via
  armband.libvirt_domain_template new state);
- _modules/virtng.py custom module;
- salt/control/virt.sls;

The new support is leveraged via our reclass model with AArch64
specific values.

Change-Id: I34bdb235cb7765ecdde365761dbd2c942f699039
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>