Import missing SVD for Atmel ATtiny/ATmega series #48
Description
Currently we are lacking the SVD files for various common Atmel AVR chips like the ATmega328.
These files can be found e.g. at https://github.com/Rahix/avr-device/tree/main/vendor, which links to http://packs.download.atmel.com/ as the source. Files are provided as ATDF files and thus need to be converted to SVD first.