Bitfields for Intel 82371FB/82371SB/82371MX motherboard IRQ Route Control:
Bit(s)	Description	)
 7	disable IRQ routing
 6	enable MIRQx/IRQx sharing
 5	(82371SB only) enable IRQ0 output
 4	reserved (0)
 3-0	ISA IRQ number to which to route the PCI IRQ
Notes:	IRQs 0-2, 8, and 13 are reserved
	interrupt sharing should only be enabled when the device connected to
	  the MIRQ line and the device connected to the IRQ line both produce
	  active high, level triggered interrupts.
SeeAlso: #01167,#01168,#01216,#01219