net: phy: broadcom: Enable 125 MHz clock on LED4 pin for BCM54612E by default.

BCM54612E have 4 multi-functional LED pins that can be configured
through register setting; the LED4 pin can be configured to a 125MHz
reference clock output by setting the spare register. Since the dedicated
CLK125 reference clock pin is not brought out on the 48-Pin MLP, the LED4
pin is the only pin to provide such function in this package, and therefore
it is beneficial to just enable the reference clock by default.

Signed-off-by: Kun Yi <kunyi@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>