phylib: Add support for board-level PHY fixups

Sometimes the specific interaction between the platform and the PHY
requires special handling.  For instance, to change where the PHY's
clock input is, or to add a delay to account for latency issues in the
data path.  We add a mechanism for registering a callback with the PHY
Lib to be called on matching PHYs when they are brought up, or reset.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>