[mtgx]

Some Linux vendors have started offering support for various "older" ARM chips, but I doubt they will even try to support all since there are many, and are not even powerful enough to be useful so there's no need and no point in doing that.

Cortex A15 is probably the most supported right now. However, I think you'll really start seeing unified support across all distros and tools starting with the 64 bit ARMv8 architecture and all the chips built on it. Everyone is working on supporting ARMv8 from day one. So you'll have to wait a bit longer for that (a year+).