[IA64] Fix iosapic interrupt delivery mode for CPE

If "CPEI Processor Override" bit is not set in "Platform Interrupt
Source Flags" in "Platform Interrupt Sources Structure" in ACPI MADT,
the target processor of CPEI is restricted to a specific CPU. Because
of this, the delivery mode for CPEI should be IOSAPIC_FIXED.

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