This method is used by both pci_io_read and pci_io_write to determine if ISA type I/O access is allowed.
The SPARSE_IO_BASE I/O address is defined. This I/O range is not defined by an I/O BAR.
Result of running IWYU (https://include-what-you-use.org/) and
applying most of the suggestions about unncessary includes and
forward declarations.
Was motivated by observing that <thread> was being included in
ppcopcodes.cpp even though it was unused (found while researching
the use of threads), but seems generally good to help with build
times and correctness.
