net: fec: add set_promisc function

Enabling promiscuous mode is necessary if FEC is the master of a DSA
switch driver where each port has their own MAC address.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/drivers/net/fec_mxc.h b/drivers/net/fec_mxc.h
index 5ccde91..62b55ef 100644
--- a/drivers/net/fec_mxc.h
+++ b/drivers/net/fec_mxc.h
@@ -272,6 +272,7 @@
 	struct clk clk_ref;
 	struct clk clk_ptp;
 	u32 clk_rate;
+	char promisc;
 };
 
 /**