net: phy: broadcom: add support for BCM54811 PHY

The BCM54811 PHY shares many similarities with the already supported BCM54810
PHY but additionally requires some semi-unique configuration.

Signed-off-by: Kevin Lo <kevlo@kevlo.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>