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>
diff --git a/drivers/net/fm/p4080.c b/drivers/net/fm/p4080.c
index 6761a2f..791caab 100644
--- a/drivers/net/fm/p4080.c
+++ b/drivers/net/fm/p4080.c
@@ -44,6 +44,12 @@
 	return port_to_devdisr[port] & devdisr2;
 }
 
+void fman_disable_port(enum fm_port port)
+{
+	ccsr_gur_t *gur = (void *)(CONFIG_SYS_MPC85xx_GUTS_ADDR);
+	setbits_be32(&gur->devdisr2, port_to_devdisr[port]);
+}
+
 phy_interface_t fman_port_enet_if(enum fm_port port)
 {
 	ccsr_gur_t *gur = (void *)(CONFIG_SYS_MPC85xx_GUTS_ADDR);