MFC 253450:
Properly handle I/O windows in bridges with the ISA enable bit set.  These
beasts still exist unfortunately.  More details can be found in other
references, but the short version is that bridges with this bit set ignore
I/O port ranges that alias to valid ISA I/O port ranges.  In the driver
this requires not allocating these alias regions from the parent device
(so they are free to be acquired by ISA devices), and ensuring no child
devices use resources from these alias regions.