PNP: introduce pnp_irq_mask_t typedef

This adds a typedef for the IRQ bitmap, which should cause
no functional change, but will make it easier to pass a
pointer to a bitmap to pnp_register_irq_resource().

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>