Instead of every "simple" target having their own duplicate file with
all the section mappings, just provide a single, simple,
"cortex-m-generic.ld" that works with our startup code and any simple
rom/ram system. This also drops the pointless copying of files all over
the place. Using -L flags properly is sufficient, and the standard file
is now in the root of the library already.
Thoughts: should this be a "sam0" family rather than samd? (Much like Atmel's
own software package lumps all the cortex-m0+ devices in one family)
This was enough to get a basic blinky working at least.