DLPX-94011 simplify kernel build and exclusion of dkms modules

[sebroy]

We currently use a mix of methods to exclude dkms (out of tree) modules from
our kernel builds. In each of the kernel repos, we have removed all of the
lines from debian.master/dkms-versions except for the line responsible for
building zfs out of tree. For preventing the zfs build, there is a
do_zfs=false debian/rules argument set in linux-pkg’s
default-package-config.sh script which works for that package.

It would be beneficial to restore the debian.master/dkms-versions files to
their original contents, as these are a source of regular merge conflicts.
Instead, we should use the debian/rules argument method from linux-pkg, which
can be shared across all linux kernel repos.

Some investigation reveals that there are two ways of excluding a dkms module
from the kernel build via a debian/rules arg:

1. setting do_<module>=false (this is how we exclude zfs, by setting
   do_zfs=false)
2. by including the module name in a dkms_exclude=<module list> argument (this
   is how we were excluding the build of v4l2loopback before that line was
   removed entirely from dkms-versions)

Using method 2 above is more compact, as all modules we need to exclude can be
included in that one argument. Setting this in linux-pkg will allow us to
restore dkms-versions in all of our linux-kernel-* repos and eliminate that
source of merge conflicts.

Once this linux-pkg PR lands, I'll move forward with simplifying our linux-kernel-*
repos.

A secondary problem I noticed in our kernel builds (and this is a problem on develop
as well as on os-upgrade) is that various calls to debian/rules are failing because
the gawk command isn't installed. This can be seen in the console output of our various
build-package jobs for the kernel repos. I've fixed that while in here.

Testing

I'm manually running a kernel build of linux-kernel-generic on an os-upgrade build server
with these linux-pkg changes in place.