x86/mm: Make {hap, shadow}_teardown() preemptible

x86/mm: Make {hap, shadow}_teardown() preemptible

A domain with sufficient shadow allocation can cause a watchdog timeout
during domain destruction.  Expand the existing -EAGAIN logic in
paging_teardown() to allow {hap/sh}_set_allocation() to become
restartable during the DOMCTL_destroydomain hypercall.

Signed-off-by: Anshul Makkar <anshul.makkar@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>
master commit: 0174da5b79752e2d5d6ca0faed89536e8f3d91c7
master date: 2015-08-06 10:04:43 +0100