meta-egvirt, templates: Add virtio-aarch64 machine

This machine is intended to run in ARMv8 virtualized environment that
provides VirtIO devices.

AGL machine configuration files are based on qemuarm64 machine from
meta-agl branch master commit e1da0efcd2eece82b0326798cfeaeb8dd48797fc.

Yocto machine configuration files are based on qemuarm64 machine from
Poky branch dunfell commit 4e931b1d05018923dc145cd97f6f965f5cb6e1a5.

Yocto Linux Kernel is used as recommended in [1]. Its metadata for the
created machine are based on qemuarm64-standard.scc from
yocto-kernel-cache branch yocto-5.4 commit
4aeda12f7f7eb84613ae1fe6e22cd9cd9790c20b.

The rationale behind creating new machine is a wish to have a machine
that could run on other hypervisor/virtual machine monitor that
implements VirtIO, not necessary QEMU. For now, virtio-aarch64 machine
runs under QEMU and OpenSynergy COQOS Hypervisor.

virtio-aarch64 machine includes following changes comparing to
qemuarm64:
* use virtio-gpu instead of VGA display (to be upstreamed to work in
  conjunction with runqemu gl, sdl, etc. options)
* use virtio-bus instead of PCI bus QEMU devices
* remove unneeded configurations

[1]: https://www.yoctoproject.org/docs/3.1.2/bsp-guide/bsp-guide.html#released-bsp-recommendations

Bug-AGL: SPEC-3668
Change-Id: Iccfee8613de63770d371a57f0caab1c1eba8d912
Signed-off-by: Vasyl Vavrychuk <vasyl.vavrychuk@opensynergy.com>