kpatch-build: revert previous module building interface

Revert the previous kpatch-build module building interface commits to
prepare for a completely different approach which builds vmlinux and all
the modules in a single pass.

This reverts commit fac9d706127ed900dd6ea7eb523914c811abac11.
This reverts commit d166fb4379fa6cdcd60553ee4d42e5fc6377b741.
kpatch-build: kpatch-build module patching support

This adds support to kpatch-build for patching modules.  It builds the
entire kernel tree, vmlinux and modules, in a single pass and then
detects which modules need to be patched.  This is the easiest case
(since the user doesn't need to care about which binaries are affected)
and the safest (since the user could be wrong).

The first build with no ccache takes a long time, but after the cache is
populated, it only takes about two minutes on my laptop.  It does take
up a TON of space in the cache now though (~/.kpatch/obj is now 8GB).

Next we can add the '-t' cmdline option for advanced users to specify
build targets.
kpatch-build: add -t option for custom build targets
kpatch-build: skip *.mod.o files

As seen on RHEL7
Merge pull request #243 from jpoimboe/kpatch-build-modules

kpatch-build: new module building interface