fm-eth: Add ability for board code to disable a port

The SoC configuration may have more ports enabled than a given board
actually can utilize.  Add a routinue that allows the board code to
disable a port that it knows isn't being used.

fm_disable_port() needs to be called before cpu_eth_init().

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

include/fm_eth.h

@@ -110,5 +110,6 @@ void fdt_fixup_fman_ethernet(void *fdt);
 phy_interface_t fm_info_get_enet_if(enum fm_port port);
 void fm_info_set_phy_address(enum fm_port port, int address);
 void fm_info_set_mdio(enum fm_port port, struct mii_dev *bus);
+void fm_disable_port(enum fm_port port);
 
 #endif