xen/sched: fix arinc653 to not use variables across cpupools

xen/sched: fix arinc653 to not use variables across cpupools

a653sched_do_schedule() is using two function local static variables,
which is resulting in bad behavior when using more than one cpupool
with the arinc653 scheduler.

Fix that by moving those variables to the scheduler private data.

Fixes: 22787f2e107c ("ARINC 653 scheduler")
Reported-by: Choi Anderson <Anderson.Choi@boeing.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Nathan Studer <nathan.studer@dornerworks.com>