[POWERPC] Generic check_legacy_ioport

check_legacy_ioport makes only sense on PREP, CHRP and pSeries.
They may have an isa node with PS/2, parport, floppy and serial ports.

Remove the check_legacy_ioport call from ppc_md, it's not needed
anymore.  Hardware capabilities come from the device-tree.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>