[TG3]: Prepare for 5750 support plus minor fixes.

1) Handle cases that apply to 5750 the same as 5705.
2) Only set CLOCK_CTRL_FORCE_CLKRUN on 5705_A0
3) Clear out on-chip and memory stats block right before
   setting MAC_MODE.
4) On bootup chip probe, always skip PHY reset if link
   is up.