xen: Switch to new irq_chip functions

Convert Xen to the new irq_chip functions. Brings us closer to enable
CONFIG_GENERIC_HARDIRQS_NO_DEPRECATED

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>