[IA64] Fix SMP Windows boot failure

[IA64] Fix SMP Windows boot failure

Sometime SMP Windows can't boot, the root cause is guest timer interrupt
is lost.

This patch fixes following issues.
1. Windows uses different way to sync itc.
2. Previously when Guest timer fires and guest ITV is masked, XEN will
   desert this Guest timer interrupt. It is not correct for windows,
   windows may expect this timer interrupt.
3. Windows may use different way to set timer in some situations.
   Windows first sets itm (which may be smaller than current itc), and
   then sets itc (which is samller than itm).
   XEN can support this way to set timer.

Signed-off-by: Anthony Xu <anthony.xu@intel.com>