Disable TX status deferral (EMACx_MR[MWSW=001]) in half-duplex mode.
I have two reports when EMAC stops transmitting when connected to a
hub. TX ring debug printouts show complete mess when this happens,
probably hardware collision handling doesn't work quite well in this
mode.

This is relevant only for SoCs with EMAC4 core (440GX, 440SP, 440SPe).
Tested on 440GX.
Signed-off-by: Eugene Surovegin <ebs@ebshome.net>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>