make on-device-installer work with pinephonepro

• New postmarketos-ondev version supports gpt: https://gitlab.com/postmarketOS/postmarketos-ondev/-/commit/ab5998de69abc149bd0740a3bc363560c8247192
• Fix the internal storage device name for the PPP

TODO:

• test that installing with "msdos" partition type still works
• test installing from emmc to emmc
• test installing from sd to emmc
• test installing from sd to sd

How to test installing from emmc to emmc:

• I tried the blockdevice mode built into tow-boot, but flashing with dd was slow (891 kb/s) and aborted after 655 MiB
• After considering other various methods, the fastest was was:
  • create the installer image (pmbootstrap install --ondev)
  • flash a regular pmOS install to SD card (e.g. with UI=console so you have networkmanager to connect to wifi etc. if needed)
  • keep the SD plugged into your computer
  • (extend the root partition to fill the whole SD card)
  • copy the installer image to the SD card, e.g. to /root/installer.img
  • plug the SD into the PPP and boot
  • login via serial
  • dd if=/root/installer.img of=/dev/mmcblk0
  • unplug the SD (otherwise the initramfs may get confused, see #1531)

I tested this with kernel 5.16.7, and it showed the pmOS splash, but then continued booting into a black screen instead of Xorg with calamares. Calamares launched though, and reacted to touch inputs, I was able to move to the next page by hitting where the continue button would be. Maybe this magically is fixed with the 5.17.9 kernel already that was just merged, we'll need to try again and fix it if needed.