[IA64] Fix domain destroy bug when multiple domains exist

[IA64] Fix domain destroy bug when multiple domains exist

Currently vmx irq handler doesn't handle IA64_IPI_VECTOR, which is
instead pended to dom0 incorrectly. That bug made people observing
system hang when destroying domU with domVTI kept running. Actually
there's no need for two different irq handlers, which should be
same as long as softirq is checked at exit path back to guest. So
remove vmx version here.

With this fix, now we can create two domains (domU+domVTI), then
destroy domU, create another domVTI, destroy domVTI with all steps
successfully finished.

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>