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/pg_wcom_expu1_update_defconfig b/configs/pg_wcom_expu1_update_defconfig
index 9029e7b..a5193cb 100644
--- a/configs/pg_wcom_expu1_update_defconfig
+++ b/configs/pg_wcom_expu1_update_defconfig
@@ -68,6 +68,8 @@
 CONFIG_ENV_ADDR_REDUND=0x60200000
 CONFIG_USE_ETHPRIME=y
 CONFIG_ETHPRIME="ethernet@2d90000"
+CONFIG_USE_HOSTNAME=y
+CONFIG_HOSTNAME="EXPU1"
 CONFIG_VERSION_VARIABLE=y
 CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_SYS_BOOTCOUNT_BE=y