Detect and only enable the port that is actually used.
The unused port, if enabled, fills up and triggers flow
control, blocking transmit and causing device timeouts.

Also enable interrupt pacing to limit interrupts at 2K/s.

Reported and fix tested by Anthony Eden.
ok dlg@

Start cleaning this driver. No functional change.
input and ok to move forward dlg@ patrick@ syl@

print version on attach

whitespace tweaks

get rid of CPSW_PRINTF

In the future, we shouldn't have one port port ARM SoC, that's just
ridiculous. This is the first step for a common and generic ARM port
for ARMv7 SoCs.