net: sgi: ioc3-eth: introduce chip start function

ioc3_init did everything from reset to init rings to starting the chip.
This change move out chip start into a new function as preparation
for easier handling of receive buffer allocation failures.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>