drivers: net: cpsw: Add reading of DT phy-handle node

Add the ability to read the phy-handle node of the
cpsw slave.  Upon reading this handle the phy-id
can be stored based on the reg node in the DT.

The phy-handle also needs to be stored and passed
to the phy to access any phy data that is available.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/cpsw.h

@@ -21,6 +21,7 @@ struct cpsw_slave_data {
 	u32		sliver_reg_ofs;
 	int		phy_addr;
 	int		phy_if;
+	int		phy_of_handle;
 };
 
 enum {