Here's some cleanups/fixes/changes for interrupts on 2.5.67 + ia64.
Specifically:

  - Cleanup some ugliness with polarity/trigger setup.

  - Add iosapic_enable_intr() to set_rte on an interupt when the
    device is enabled.  IMHO, we really only want to unmask RTEs
    for PRTs we might actually use.  This moves the interrupt
    distribution here too.

  - When changing a vector from edge to level, call register_intr()
    to do it so all the data structures get set correctly.  If we
    have to guess how to setup an interupt and get it wrong, this
    should close some holes in changing it back to the correct type.

  - Register the HCDP interrupt in 8250_hcdp - this is where we have
    to guess the polarity/trigger.  The real handler will get fixed
    up via PCI setup or ACPI namespace serial support, this gets it
    associated w/ the port at setup.  This should allow interrupts
    to work when using builtin UARTs as console on HP Itanium2 boxes.