[SRU][D/C/B/X linux-kvm][PATCH v2] UBUNTU: [Config]: enable KEXEC and KEXEC_FILE

[Connor Kuehl]

BugLink: https://bugs.launchpad.net/bugs/1799791

== SRU Justification ==

The enablement of these options could allow for some creative
applications of linux-kvm.

The launchpad bug mentions Cosmic, but for consistency I've also named
Disco, Bionic, and Xenial.

Note: Xenial's patch required just a little more work, but not much.

== Regression Potential ==

Low. This enables a config change for a derivative. The config is already
enabled in the generic/master.

== Test Case ==

Ran "cranky updateconfigs" to make sure the config changes applied cleanly.
Compile-tested all architectures for each series with this patch applied.

Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>