include: phy: add data field for private driver data

This is useful to carry custom information between the driver structure
associated with a specific HW and the driver code.

Signed-off-by: Alex Marginean <alexandru.marginean@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/phy.h

@@ -115,6 +115,9 @@ struct phy_driver {
 			 u16 val);
 
 	struct list_head list;
+
+	/* driver private data */
+	ulong data;
 };
 
 struct phy_device {