net: phy: Add support for Broadcom Omega internal Combo GPHY

Add support for the Broadcom Omega SoC internal Combo Ethernet
GPHY to the bcm7xxx phy driver.

Signed-off-by: Arun Parameswaran <arun.parameswaran@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>