PHYLIB: Add 1000Base-X support for Broadcom bcm5482

Configure the BCM5482S secondary SerDes for 1000Base-X mode when the
appropriate dev_flags are passed in to phy_connect().  This is
needed when the PHY is used for fiber and backplane connections.

Signed-off-by: Nate Case <ncase@xes-inc.com>
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>