Move PioPort timing code into Simple Timing Port object

Move PioPort timing code into Simple Timing Port object
Make PioPort use it
Make Physical memory use it as well

src/SConscript:
    Add timing port to sconscript
src/dev/io_device.cc:
src/dev/io_device.hh:
    Move simple timing pio port stuff into a simple timing port class so it can be used by the physical memory
src/mem/physical.cc:
src/mem/physical.hh:
    use a simple timing port stuff instead of rolling our own here

--HG--
extra : convert_revision : e5befbd295a572568cfdca533efb5ed1984c59d1