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/MPC837XERDB_defconfig b/configs/MPC837XERDB_defconfig
index a227ca8..7287ca6 100644
--- a/configs/MPC837XERDB_defconfig
+++ b/configs/MPC837XERDB_defconfig
@@ -148,6 +148,7 @@
 CONFIG_LCRR_DBYP_PLL_BYPASSED=y
 CONFIG_LCRR_CLKDIV_8=y
 CONFIG_FSL_SERDES=y
+CONFIG_USE_UBOOTPATH=y
 CONFIG_SYS_MONITOR_LEN=524288
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
@@ -178,6 +179,10 @@
 CONFIG_BOOTFILE="uImage"
 CONFIG_USE_ETHPRIME=y
 CONFIG_ETHPRIME="TSEC0"
+CONFIG_USE_HOSTNAME=y
+CONFIG_HOSTNAME="mpc837x_rdb"
+CONFIG_USE_ROOTPATH=y
+CONFIG_ROOTPATH="/nfsroot"
 CONFIG_FSL_SATA=y
 CONFIG_SYS_SATA_MAX_DEVICE=2
 CONFIG_SYS_BR0_PRELIM_BOOL=y