[IA64] Enable percpu vector domain for IA64_GENERIC

Add per-CPU vector domain support for IA64_GENERIC. It is enabled by
adding the "vector=percpu" boot option.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>