Adafruit Trinket M0 Bossac Offset is Wrong

[psidhu]

Describe the bug
When using bossac to flash the adafruit_trinket_m0, it defaults to the 0x0000 address. This is wrong due to the UF2 bootloader. See https://learn.adafruit.com/adafruit-trinket-m0-circuitpython-arduino/uf2-bootloader-details#running-bossac-on-the-command-line-46-29.

Also, due to #13151 (code,partition not taking effect unless BOOTALODER_MCUBOOT is set), simply fixing the bossac offset isn't enough. The physical location of where the application is flashed must change.

Note that adafruit ships these locked now: https://forums.adafruit.com/viewtopic.php?f=57&t=142170&p=707151#p707153

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=adafruit_trinket_m0
3. make
4. make flash
5. see error

Expected behavior
For bossac to flash to the correct address for this board.

Impact
Showstopper as no one can flash this board with make flash

[ixmeins]

I used the Adafruit board as a basis for my homegrown SAMR21 board and I noticed this, as well as the defaults for my particular selected chip (now that R21 support is built in) being wrong with a default start address of 0x0000, 256kb flash and 32k ram where as my chip is 128/16. I also used a modified Adafruit bootloader so also needed the 0x2000 start.
I get around it by resetting those values (ninja menuconfig general architecture options) but then I use the UF2 method to program as I could not get bossac to response via ninja flash.

[sslupsky]

see #20740