tests/qtest: option to suspend during migration

tests/qtest: option to suspend during migration

Add an option to suspend the src in a-b-bootblock.S, which puts the guest
in S3 state after one round of writing to memory.  The option is enabled by
poking a 1 into the suspend_me word in the boot block prior to starting the
src vm.  Generate symbol offsets in a-b-bootblock.h so that the suspend_me
offset is known.  Generate the bootblock for each test, because suspend_me
may differ for each.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/1704312341-66640-11-git-send-email-steven.sistare@oracle.com
Signed-off-by: Peter Xu <peterx@redhat.com>