Prep for Pi 5 support

Few tracking info to figure-out what it will take to support that new beast coming-up with new bcm2712_defconfig option
https://github.com/raspberrypi/linux/pull/5618

Checklist:

• aports: main/linux-rpi: refactor flavors as per #15324 (closed).
• aports: main/zfs-rpi: check/sync flavors with linux-rpi
• aports: community/jool-modules-rpi: check/sync flavors with linux-rpi
• aports: main/raspberrypi-bootloader: minimal change for [Pi5] filter in config.txt (second-stage bootloader in EEPROM)
• aports: main/raspberrypi-bootloader: add trigger script to generate config.txt.
• aports: main/linux-firmware: wifi and bluetooth firmware are same as Pi4: new Pi5 aliases are in
• alpine-conf: setup-disk: adapt to linux-rpi configs changes (-config.txt)
• aports: scripts/mkimg.arm.sh: adapt to linux-rpi configs changes (updated config.txt).
• aports: main/mesa: upgrade to 23.3.0 with newer Pi5 GPU support (stable 23.3.1 is expected 2023-12-13)
• other?

@ncopa