MII: fix Kconfig dependencies for MII

MII Kconfig option is apart of the core networking drivers and
by default NET_CORE is enabled so drivers selecting MII will
have MII enabled as well.  It was found using the randconfig
option during testing, MII would be selected but NET_CORE
could be disabled.  This caused a dependency error.

Resolved the dependency by selecting NET_CORE when MII is
selected.

Reported-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/renesas/Kconfig b/drivers/net/ethernet/renesas/Kconfig
index f57ae23..9755b49 100644
--- a/drivers/net/ethernet/renesas/Kconfig
+++ b/drivers/net/ethernet/renesas/Kconfig
@@ -9,6 +9,7 @@
 		 CPU_SUBTYPE_SH7763 || CPU_SUBTYPE_SH7619 || \
 		 CPU_SUBTYPE_SH7724 || CPU_SUBTYPE_SH7757)
 	select CRC32
+	select NET_CORE
 	select MII
 	select MDIO_BITBANG
 	select PHYLIB