x86: Change Xen hypervisor's interrupt infrastructure

x86:  Change Xen hypervisor's interrupt infrastructure
from vector-based to IRQ-based.

In per-cpu vector environment, vector space changes to
multi-demension resource, so vector number is not appropriate
to index irq_desc which stands for unique interrupt source. As
Linux does, irq number is chosen to index irq_desc. This patch
changes vector-based interrupt infrastructure to irq-based one.
Mostly, it follows upstream linux's changes, and some parts are
adapted for Xen.

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>