xen: events: push setup of irq<->{evtchn,ipi,virq,pirq} maps into irq_info init functions

Encapsulate setup of XXX_to_irq array in the relevant
xen_irq_info_*_init function.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>