Enable LZMA compression for arm64 kernel Image with Depthcharge

The arm64 kernel Image files are not compressed as part of the kernel
build.  It can be done separately and it is up to the bootloader to
handle decompression.  As Depthcharge supports LZMA for arm64 kernels,
enable this feature to significantly reduce the size of the resulting
FIT image.

This is especially useful to keep the Depthcharge TFTP buffer size
small while being able to boot kernels that would be too big if
uncompressed.

Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>
15 jobs for T15486-depthcharge-arm64-lzma in 10 minutes and 34 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #53678
amd64
dispatcher-debian-10

00:02:49

passed #53676
amd64
dispatcher-debian-9

00:03:10

passed #53679
amd64
server-debian-10

00:02:04

passed #53677
amd64
server-debian-9

00:02:28

 
  Analyze
passed #53681
amd64
black

00:00:28

passed #53683
amd64
code_quality

00:00:20

passed #53682
amd64
codestyle

00:00:34

passed #53685
amd64
job-schema

00:00:39

passed #53684
amd64
pylint

00:02:15

passed #53680
amd64-dind allowed to fail
sast

00:01:25

 
  Build
passed #53688
amd64
amd64/pkg-debian-10

00:01:15

passed #53687
amd64
amd64/pkg-debian-9

00:01:38

passed #53686
amd64
doc

00:01:15

 
  Docker
passed #53689
amd64-dind
amd64/lava-dispatcher

00:03:05

passed #53690
amd64-dind
amd64/lava-server

00:03:29