Add support for AArch64/ARM64 EFI architecture (#1757)

* Add AArch64/ARM64 EFI boot support (for QEMU and some boards)
* Allow GRUB to load cmdline.txt-like
* Enable qcow2/vmdk disk images

Co-authored-by: Stefan Agner <stefan@agner.ch>

Documentation/boards/generic-aarch64/README.md

@@ -0,0 +1,36 @@
+# Generic aarch64
+
+## Supported Hardware
+
+This board configuration aims to support most aarch64 systems with UEFI boot
+Hardware it has been tested with is listed below.
+
+## Tested Hardware
+
+| Device                | Release Date | Support | Config      |
+|-----------------------|--------------|---------|-------------|
+| QEMU                  | QEMU         | yes     | [generic_aarch64](../../../buildroot-external/configs/generic_aarch64_defconfig) |
+
+
+## Requirements
+
+- aarch64 support
+- UEFI boot
+
+## Wifi
+
+WiFi is untested.
+
+## Bluetooth
+
+Bluetooth is untested.
+
+## Installation
+
+Make sure secure boot is disabled in the UEFI BIOS settings.
+
+Currently there is no shiny installation method. Checklist:
+- Boot PC to live environment using PXE or USB
+- Copy or download the Home Assistant OS image into your live environment
+- unxz the image and dd to the local hard disk
+- Reboot