Add samg series devices

[mcbridejc]

Adds support for the devices in the SAMG device data pack.

Some changes to support differences that popped up in this pack:

• Some, but not all, parts in the pack have a variant field at the end of the part number. To accomodate, the variant field is allowed to be an empty string.
• The memory region names are different and not all have an rw attribute, so a default ('r') is provided

For peripherals, I haven't done a thorough comparison but so far every peripheral I've looked at is different from the samd5x/samd2x devices. I've chosen to put the family/series (e.g. "samg55") as the peripheral type for all samg family parts, and leave it as "sam" for everything else, just as it was. I think there is peripheral overlap between e.g. samg54 and samg55, but I haven't gone over it in detail and my thinking is that a driver can declare support for multiple parts if the driver author confirms they are all supported.

[salkinium]

my thinking is that a driver can declare support for multiple parts if the driver author confirms they are all supported.

Yes, definitely. The grouping of driver type is currently done manually, ideally it should be based on some mathematical set/subset grouping of register maps, to reduce the comparison scope, but I haven't gotten there yet. 🤷‍♂️