Add mlx5_core driver to support ConnectX-4 devices

Adds a 170K module and allows usage of 25/100GbE adapters.
diff --git a/openpower/configs/linux/skiroot_defconfig b/openpower/configs/linux/skiroot_defconfig
index b76ecb8..6b20799 100644
--- a/openpower/configs/linux/skiroot_defconfig
+++ b/openpower/configs/linux/skiroot_defconfig
@@ -139,6 +139,7 @@
 CONFIG_IXGB=m
 CONFIG_IXGBE=m
 CONFIG_MLX4_EN=m
+CONFIG_MLX5_CORE=m
 CONFIG_MYRI10GE=m
 CONFIG_QLGE=m
 CONFIG_NETXEN_NIC=m