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.
This is not strictly required, as this part is supported by the
devices.data linker script generator tool. However, as we're still in
migration for that tool, and this is the first time we're getting proper
lm3s(qemu) support, keep it for now.
