[IA64] Final patch to make evtchn fully working for xen/ia64

[IA64] Final patch to make evtchn fully working for xen/ia64

OK, this is the last one of patch sets, which enables xen/ia64 to work
on event channel mechanism fully. Now user may observe /proc/interrupts
of dom0 as:

           CPU0
 34:         12        Phys-irq  ide0
 39:          0        Phys-irq  acpi
 45:        322        Phys-irq  serial
 48:     115006        Phys-irq  peth0
 49:      16269        Phys-irq  ioc0
 50:         31        Phys-irq  ioc1
 51:          2        Phys-irq  ehci_hcd:usb1
 52:          0        Phys-irq  uhci_hcd:usb2
 53:         55        Phys-irq  uhci_hcd:usb3
256:          0     Dynamic-irq  RESCHED0
257:          0     Dynamic-irq  IPI0
258:      44572     Dynamic-irq  timer0
259:       2316     Dynamic-irq  xenbus
260:       8304     Dynamic-irq  blkif-backend
261:      25947     Dynamic-irq  vif3.0
ERR:          0

Based on this patch, dom0's performance is not affected, while domU's
network output is seen with several percents increase. More important,
now xen/ia64 can progress a base step towards driver domain support!

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