xen_vector_callback_enabled is x86 specific and supporting evtchn rebind
on others architectures may be different.
Introduce a new helper to check if we can rebind the event channel.
Note that xen_intr_assign_cpu was only checking if
xen_vector_callback_enabled. Although it looks like to me that rebind
should be supported for PVH.
Submitted by: Elliott Mitchell <firstname.lastname@example.org>
Original implementation: Julien Grall <email@example.com>, 2015-10-10 12:40:06