Draft: add Sony Xperia 10 III port

This is an initial attempt at porting PostmarketOS to the Sony Xperia 10 III, following the steps at https://wiki.postmarketos.org/wiki/Porting_to_a_new_device

The current status is that it first shows the bootloader unlocked screen which says it can't verify for corruption, followed by a screen saying the device is corrupt.

Steps to reproduce:

1. This devices was unlocked and flashed with SailfishOS following these instructions https://jolla.com/how-to-install-sailfish-x-on-xperia-10-iii-on-linux/
2. flash configuration was extracted from the hybris-boot.img Sailfish image
3. values were experimentally adjusted from https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/arch/arm64/boot/dts/qcom/sm6350-sony-xperia-lena-pdx213.dts?id=ed1648d52a375e606a0c88f5bf65282686ae6541
4. hold the volume up button, insert USB cable, to enter fastboot
5. pmbootstrap flasher flash_rootfs
6. pmbootstrap flasher flash_kernel
7. pmbootstrap chroot
8. avbtool make_vbmeta_image --flags 2 --padding_size 4096 --output /vbmeta.img
9. fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img
10. fastboot --disable-verity --disable-verification flash vbmeta_system vbmeta.img
11. fastboot erase dtbo
12. fastboot reboot

So this phone is clearly unlocked since it ran SailfishOS, but from my cursory understanding the second screen suggests there might be a AVB failure somehow? Is one of my partitions still wrong, or could it be at a point already where it's a problem with the kernel?

Konrad Dybcio in the linked kernel commit clearly achieved a booting kernel on this device, but says the bootloader is "VERY unpleasant". I'm unfortunately at a loss what I'm missing or how to debug the error in more detail.

Hence this draft PR, maybe someone more knowledgeable than me can suggest a way forward?