PHY: add BCM5464 support to broadcom PHY driver

The BCM5464 can be used with the current broadcom PHY driver
by just adding the appropriate chip ID and using the existing
support within.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>