armvirt: 64: add support for other SystemReady-compatible vendors

armvirt: 64: add support for other SystemReady-compatible vendors

These changes are to support other vendors that have SystemReady/EFI
support, including:
* Marvell Armada
** (This is speculative as I don't have a machine of my own to test)
* Amazon Graviton (tested bare-metal and virtualized instances)
* VMware (Fusion for ARM Mac preview)
* NXP/Freescale (Layerscape series not already selected)
* HiSilicon
* Allwinner/sunxi
* Rockchip (untested, options taken from arm64 defconfig)

To give an idea of the hardware certified for SystemReady,
see
https://www.arm.com/architecture/system-architectures/systemready-certification-program/ir
and
https://www.arm.com/architecture/system-architectures/systemready-certification-program/es

Other vendors that _should_ work include Marvell Octeon 10
and Ampere. I understand these systems should work
"out of the box" in ACPI mode but may require other drivers
(e.g PCIe NICs and storage controllers).

Signed-off-by: Mathew McBride <matt@traverse.com.au>