Kpatch build module support

This commit adds support for module patching with kpatch-build.
It introduces a new option, -t/--targets, that allows the user to
specify kernel make targets that are impacted by the patch.  These
targets will be examined by kpatch-build for changes.

While this approach requires the user to provide more information to
kpatch-build about what exactly has changed, it is better that
rebuilding the entire source tree (make vmlinux && make modules) which
would dramatically increase the runtime and disk space requirements of
using kpatch-build.

Future improvements could include a script that will independently
generate the targets list file.