[ARM] Introduce arm64 CPU support

This is the main patch for arm64 or armv8 or aarch64 CPU support.

This new arm64 port is very much in-line with arm32ve port because
the arm64 virtualization extensions is just 64-bit version of arm32ve
virtualization extensions.

Signed-off-by: Sukanto Ghosh <sukantoghosh@gmail.com>
[ARM] Introduce virt-v8 guest template for arm64 guest

There are no real development boards openly available for arm64
hence we introduce a completely paravirtualized virt-v8 guest
for folks interested in having a dummy or paravirtualized
hardware for guest.

This virt-v8 guest is a virtual machine with VirtIO-based
devices, GIC and ARMv8 generic timer.

This patch adds guest template for virt-v8 guest.

Signed-off-by: Sukanto Ghosh <sukantoghosh@gmail.com>
[ARM] Introduce generic armv8 board

With the new arm64 (or armv8) port we try to implement unified
Xvisor binary for all arm64 boards.

To achieve this we introduce generic armv8 board which is fully
device tree based (i.e. DTB-based) similar to linux arm64 port.

The only constraint with generic armv8 board support is that
actual HW board on which Xvisor runs should have GICv2 or higher
as PIC.

Signed-off-by: Sukanto Ghosh <sukantoghosh@gmail.com>
[DOCS] Add light-weight bootwrapper for ARMv8 foundation models

This patch adds light-weight and minimalistic bootwrapper assembly
source for booting Xvisor on ARMv8 foundation models.

In simpler words, it is a minimalistic bootloader for launching
Xvisor on ARMv8 foundation model.

Signed-off-by: Sukanto Ghosh <sukantoghosh@gmail.com>
[TESTS] Add arm64 basic firmware for virt-v8 guest

We need a Xvisor friendly firmware/bootloader for Virt-v8 guest which
will help us launch Guest OSes on Virt-v8 guest and also help us do
some testing of virtual CPU emulated by Xvisor ARM64.

This patch adds arm64 basic firmware for Virt-v8 Guest which is very
similar to arm32 basic firmware for VExpress-A15 Guest. This firmware
is capable of booting upstream arm64 linux kernel.

Signed-off-by: Sukanto Ghosh <sukantoghosh@gmail.com>