Convert CONFIG_HOSTNAME et al to Kconfig

This converts the following to Kconfig:
   CONFIG_GATEWAYIP
   CONFIG_HOSTNAME
   CONFIG_IPADDR
   CONFIG_NETMASK
   CONFIG_ROOTPATH
   CONFIG_SERVERIP
   CONFIG_UBOOTPATH

To do this, we introduce a CONFIG_USE_ form of each of the above and
change include/env_default.h to test for that to be set before setting a
value. Further, we don't want to stringify the IP address related values
as they are now properly strings via Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/M5235EVB_defconfig b/configs/M5235EVB_defconfig
index cb5bcb7..255f3b9 100644
--- a/configs/M5235EVB_defconfig
+++ b/configs/M5235EVB_defconfig
@@ -34,7 +34,17 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_USE_BOOTFILE=y
 CONFIG_BOOTFILE="u-boot.bin"
+CONFIG_USE_HOSTNAME=y
+CONFIG_HOSTNAME="M5235EVB"
 CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
+CONFIG_USE_GATEWAYIP=y
+CONFIG_GATEWAYIP="192.162.1.1"
+CONFIG_USE_IPADDR=y
+CONFIG_IPADDR="192.162.1.2"
+CONFIG_USE_NETMASK=y
+CONFIG_NETMASK="255.255.255.0"
+CONFIG_USE_SERVERIP=y
+CONFIG_SERVERIP="192.162.1.1"
 CONFIG_SYS_RX_ETH_BUFFER=8
 CONFIG_SYS_I2C_LEGACY=y
 CONFIG_SYS_I2C_FSL=y