x86/mm: When mem event automatically promotes access rights, let other subsystems...

x86/mm: When mem event automatically promotes access rights, let other subsystems know

The mem event fault handler in the p2m can automatically promote the access
rights of a p2m entry. In those scenarios, vcpu's are not paused and they will
immediately retry the faulting instructions. This will generate a second fault
if the underlying entry type requires so (paging, unsharing, pod, etc).
Collapse the two faults into a single one.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>