Our AVR port doesn't make use of an ISR stack and just victimizes the
stack of whatever thread happens to be running, which in most cases is
the idle thread. Hence, the idle stack has to be large enough to
support the ztimer ISR.
Add ATxmega common files and cpu definitions.
This works was originally developed by @Josar. The 2018 version
were port to 2021 mainline.
This version changes original port to have only the atxmega CPU
definition. With that, all family can be accomodated.
Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>
