Make it possible to scan multiple scanlists together (1+2, 1+3, and 2+3)

[areksh]

Small changes to make it possible to scan multiple scanlists, and associated README updates.

Buttons have new functionality when scanning channels:

4 - scan channels on list 1 and 2
5 - scan channels on list 1 and 3
6 - scan channels on list 2 and 3

The other keys have been moved down like so:

7 - scan 1, 2, 3
8 - scan all

Tested by making a build on Gtihub codespaces and flashing it on my radio. On this radio I assigned PMR1-4 to scanlist 1, 5-8 to scanlist 2, and 9 to 12 to scanlist 3. Using a second radio I then transmitted on each PMR frequency while having different scanlist settings enabled and the behaviour was as expected.

[areksh]

Basic build is too big as a result of this change:

☘️ Basic compilation...
/usr/lib/gcc/arm-none-eabi/14.2.0/../../../../arm-none-eabi/bin/ld: f4hwn.basic section `.text' will not fit in region `FLASH'
/usr/lib/gcc/arm-none-eabi/14.2.0/../../../../arm-none-eabi/bin/ld: region `FLASH' overflowed by 68 bytes

[armel]

Basic build is too big as a result of this change:

☘️ Basic compilation...
/usr/lib/gcc/arm-none-eabi/14.2.0/../../../../arm-none-eabi/bin/ld: f4hwn.basic section `.text' will not fit in region `FLASH'
/usr/lib/gcc/arm-none-eabi/14.2.0/../../../../arm-none-eabi/bin/ld: region `FLASH' overflowed by 68 bytes

Indeed, it's a problem 🤭

This kind of feature should ideally be available in all editions.
By the way, this will also have an impact on the Chirp driver...

I'll look into this PR later.

Armel, F4HWN