[IA64] Fix ISA IRQ trigger model and polarity setting

When handling Interrupt Source Override in MADT table, the default
ISA IRQ trigger model and polarity should be edge-rising.
Current IA64 implmentation doesn't follow the specification and
set default ISA IRQ trigger model as level-low. With that wrong
configuration and when system runs out of interrupt vectors,
it will cause vector sharing among edge triggered ISA IRQ and
level triggered PCI IRQ, then interrupt storm. So change the code
to follow the specification.

Signed-off-by: Liu Jiang <jiang.liu@huawei.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>