Fix: AT32F43x cleanup

[ALTracer]

Detailed description

• The bank_split field of struct at32f43_flash can be eliminated from _probe/_add_flash if I can use a different method of accessing second bank in _mass_erase, checking that target->flash->next list has a non-NULL entry. No other functions need it because BMD API guarantees no operations span multiple banks. This change was rebased past AT32F405 merge.
• Also, hook the STM32-generic UID printing command to this driver and introduce a meson dependency between these TUs. Move the macros for "engineering bytes"/UID into its own group.

Verified on AT-START-F437 to not break flashloading, a firmware spanning two banks was used.
This should bring a minor reduction to target_flash priv size, and it's a preparation to refactoring this driver to carry USD_BASE and FPEC_BASE in that priv such that targets in stm32f1.c can be migrated here.

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues

[dragonmux]

This all looks reasonable, merging once rebased on main. In regards the mass erase point, once Perigoso's #1619 is merged, you'll be able to specify the mass erase function as flash->mass_erase, setting it to the bank mass erase function, and eliminating the custom mass erase implementation. That'll solve the bank split headache properly.

Thank you for the contribution!