fman/mEMAC: set SETSP bit in IF_MODE regisgter for RGMII speed

Some legacy RGMII phys don't have in band signaling for the
speed information. so set the RGMII MAC mode according to
the speed got from PHY.

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Reported-by: John Traill <john.traill@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>