[IA64] Add support to physdev_ops

[IA64] Add support to physdev_ops

Add support to physdev ops, and thus give IOSAPIC RTEs
managed by Xen now. Dom0 now issues hypercall to r/w
RTE entry. Another change is the irq vector allocation
which is also owned by xen now.

After this change, the IOSAPIC is almost owned by xen
with only exception as IOSAPIC EOI which is still issued
by dom0 directly. But that's OK since currently dom0
owns all external physical devices. Later full event
channel mechanism will provide necessary support for
driver domain, and at that time, dom0 instead issues
physdev_op (PHYSDEVOP_IRQ_UNMASK_NOTIFY) naturally as
replace of IOSAPIC EOI.

Signed-off-by Kevin Tian <kevin.tian@intel.com>