BCM54210E/BCM50212E has been verified to work correctly with the
auto-power down configuration done by bcm54xx_adjust_rxrefclk(), add it
to the list of PHYs working.

While we are at it, provide an appropriate name for the bit we are
changing which disables the RXC and TXC during auto-power down when
there is no energy on the cable.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>