net: phy: broadcom: Add support for BCM54612E

This PHY has internal delays enabled after reset. This clears the
internal delay enables unless the interface specifically requests them.

Signed-off-by: Xo Wang <xow@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>