meta-zarhus-bsp-qemuarm-uboot: Add qemuarm-uboot machine

[m-iwanicki]

Allows building image that can run on QEMU (with U-Boot). Might be useful for testing and development.

U-Boot:

$ qemu-system-arm -device virtio-net-device,netdev=net0 -netdev user,id=net0,hostfwd=tcp:127.0.0.1:2222-:22 \
    -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 \
    -drive id=disk0,file=zarhus.img,if=none,format=raw -device virtio-blk-device,drive=disk0 -device qemu-xhci \
    -device usb-tablet -device usb-kbd -machine virt,highmem=off -cpu cortex-a15 -smp 4 -m 1G \
    -serial mon:stdio -serial null -nographic -device virtio-gpu-pci -bios u-boot.bin -kernel zImage \
    -append 'root=PARTLABEL=root rw ip=dhcp console=ttyAMA0 console=hvc0 swiotlb=0'


U-Boot 2024.01 (Jan 08 2024 - 15:37:48 +0000)

DRAM:  1 GiB
Core:  52 devices, 14 uclasses, devicetree: board
Flash: 64 MiB
Loading Environment from Flash... *** Warning - bad CRC, using default environment

In:    serial,usbkbd
Out:   serial,vidconsole
Err:   serial,vidconsole
Bus xhci_pci: Register 8001040 NbrPorts 8
Starting the controller
USB XHCI 1.00
scanning bus xhci_pci for devices... 3 USB Device(s) found
Net:   eth0: virtio-net#31
Hit any key to stop autoboot:  0
=> version
U-Boot 2024.01 (Jan 08 2024 - 15:37:48 +0000)

arm-zarhus-linux-gnueabi-gcc (GCC) 13.2.0
GNU ld (GNU Binutils) 2.42.0.20240216
=>

With splash enabled (video): #60 (comment)

---

This PR was also tested with #67 (rootfs encryption):

qemuarm-uboot:~$ sudo cryptsetup status /dev/disk/by-label/root
/dev/disk/by-label/root is active and is in use.
  type:    LUKS2
  cipher:  aes-xts-plain64
  keysize: 512 bits
  key location: keyring
  device:  /dev/vda9
  sector size:  512
  offset:  32768 sectors
  size:    1774528 sectors
  mode:    read/write