add support for delaying pio writes until the cache access occurs

add support for delaying pio writes until the cache access occurs

dev/ns_gige.cc:
    add support for delaying pio writes until the cache access occurs
    the only write we delay are for CR_TXE and CR_RXE
dev/sinic.cc:
dev/sinic.hh:
    the txPioRequest and rxPioRequest things were more or less bogus
    add support for delaying pio writes until the cache access occurs
dev/sinicreg.hh:
    Add delay_read and delay_write to the register information struct
    for now, we won't delay any reads, and we'll delay the writes that
    initiate DMAs
python/m5/objects/Ethernet.py:
    add a parameter to delay pio writes until the timing access
    actually occurs.

--HG--
extra : convert_revision : 79b18ea2812c2935d7d5ea6eff1f55265114d05d