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

[Connor Kuehl]

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

== SRU Justification ==

This option was initially turned off as part of the minimal KVM config.
However, it is enabled in the master/generic config and its enablement
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.

== Regression Potential ==

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

== Test Case ==

Compile-tested all architectures for each series with this patch applied.

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