Add distribution targets that populate a directory with output files
from the corresponding kernel build.

That target can be run with
  $ bazel run //common:kernel_dist -- --dist_dir=$DIST_DIR --flat

That expands to //common:kernel_aarch64_dist and when run it popoulates
$DIST_DIR with the build artifacts. Adding --flat strips the prefix from
the output directory, such that ./common/kernel_aarch64/vmlinux becomes
just ./vmlinux.

Bug: 197842210
Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: Ic385c6cc2cc13b0b044020d415006ec5ea22966a