net: fec: sharing MDIO for two enet controllers

On i.MX6SX, 6UL and 7D, there are two enet controllers each has a
MDIO port. But Some boards share one MDIO port for the two enets. So
introduce a configuration CONFIG_FEC_MXC_MDIO_BASE to indicate
the MDIO port for sharing.
In Kconfig, user needs enable CONFIG_FEC_MXC_SHARE_MDIO first to enter
the CONFIG_FEC_MXC_MDIO_BASE.

To i.MX28, adapt to use the new config

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 98573cb..3a374d8 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -155,9 +155,20 @@
 	help
 	  This MAC is present in OpenRISC and Xtensa XTFPGA boards.
 
+config FEC_MXC_SHARE_MDIO
+	bool "Share the MDIO bus for FEC controller"
+	depends on FEC_MXC
+
+config FEC_MXC_MDIO_BASE
+	hex "MDIO base address for the FEC controller"
+	depends on FEC_MXC_SHARE_MDIO
+	help
+	  This specifies the MDIO registers base address. It is used when
+	  two FEC controllers share MDIO bus.
+
 config FEC_MXC
 	bool "FEC Ethernet controller"
-	depends on MX5 || MX6
+	depends on MX5 || MX6 || MX7
 	help
 	  This driver supports the 10/100 Fast Ethernet controller for
 	  NXP i.MX processors.