This fixes the jumbo frame support on EMAC V4 systems. Now the correct
bit is set depending on the EMAC version configured.

Tested on Kilauea (405EX) and Canyonlands (460EX).
Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>