Improve the functionality of the PORTS_MODULES knob by adding
LOCALBASE/bin and sbin to PATH, which allows dependencies to be found;
adding SRC_BASE and OSVERSION to match the new kernel, and putting the
related builds under MAKEOBJDIRPREFIX so that they only need to be built
once per kernel.

In addition to the PR this includes ideas/contributions from crees
and matthew.

PR: ports/161452
Submitted by: Garrett Cooper <yanegomi@gmail.com>