Rather than having one global instance, let's permit multiple instances
of sercomm to co-exist, with all API functions extended by the instance
as first argument.
Change-Id: I0f3b53f464b119d65747bcb0be0af2d631e1cc05
This imports the file src/target/firmware/comm/sercomm.c from
osmocom-bb.git without introducing any modifications. It will not even
be built yet, as Makefile integration is intentionally left until it has
been adapted to work inside libosmocore.
Change-Id: I9ee199381c7b5986a9540d124836cdddd0f66c86