PlatformIO can not add custom processor

[maxgerhardt]

@trampas

It should be such that I can include links to my compiler build tools, SVD, packs and such in the platform.ini and not have to do pull request into platformIO main repo to make this happen

One does not have to do all that. We’ve demonstrated that at Bare metal on arduino due / atmelsam. Custom board definition + a tiny bit of builder script in a baremetal project get CMSIS up and running just fine.