linux: Re-enable mlx5 driver

With recent v4.4.x stable releases and updated card firmware, mlx5
network devices now appear to behave properly over kexec.

Reverts: e76515434c0b83acf4bfba467a4940e10c6ac67f
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/linux/skiroot_defconfig b/openpower/configs/linux/skiroot_defconfig
index afee3a2..8d0bd35 100644
--- a/openpower/configs/linux/skiroot_defconfig
+++ b/openpower/configs/linux/skiroot_defconfig
@@ -139,8 +139,9 @@
 CONFIG_E1000E=m
 CONFIG_IXGB=m
 CONFIG_IXGBE=m
-CONFIG_NET_VENDOR_MELLANOX=y
 CONFIG_MLX4_EN=m
+CONFIG_MLX5_CORE=m
+CONFIG_MLX5_CORE_EN=y
 CONFIG_MYRI10GE=m
 CONFIG_QLGE=m
 CONFIG_NETXEN_NIC=m