[XEN] Get rid of many uses of domain_crash_synchronous().

[XEN] Get rid of many uses of domain_crash_synchronous().

It is much more dangerous than domain_crash() because it
stops execution of teh current context regardless of
current state (e.g., IRQs disabled, locks held).

The preferred method to crash a domain is domain_crash()
and error return to the caller.

Signed-off-by: Keir Fraser <keir@xensource.com>