powerpc/86xx: mpc8610_hpcd: fix interrupt trigger type for ULi IDE

i8259 PIC is disabled on MPC8610HPCD, and ULi IDE is configured to use
PCI sideband interrupt that is specified in the device tree.

Current HPCD's device tree specify that IDE interrupt is low to high
sensitive, but in practice ULi IDE throws active-high interrupts (not
active-low as all normal PCI devices).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>