automation: Add a new job for testing boot time cpupools on arm64

automation: Add a new job for testing boot time cpupools on arm64

Add a new test job qemu-smoke-arm64-gcc-boot-cpupools that will execute
script qemu-smoke-arm64.sh to test boot time cpupools feature.
Enable CONFIG_BOOT_TIME_CPUPOOLS for the arm64 build and add a new test
case in qemu-smoke-arm64.sh that if selected will make use of the
ImageBuilder feature to create cpupool with cpu@1, null scheduler and
assign it to domU. Add a check in dom0 xen.start to see if domU is
assigned a Pool-1 with null scheduler.

Take the opportunity to refactor the qemu-smoke-arm64.sh script as
follows:
 - use domU_check to store the test's commands to be run from domU
 - use dom0_check to store the test's commands to be run from dom0
 - use fdtput instead of sed to perform dtb modifications
 - use more meaningful messages for "passed" variable. This way we can
   grep for messages reported either by domU or dom0 and get rid of
   assumption that tests can only be run from domU

Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>