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/qemu-ppce500_defconfig b/configs/qemu-ppce500_defconfig
index cdad1b0..a19d555 100644
--- a/configs/qemu-ppce500_defconfig
+++ b/configs/qemu-ppce500_defconfig
@@ -8,6 +8,7 @@
 CONFIG_TARGET_QEMU_PPCE500=y
 CONFIG_ENABLE_36BIT_PHYS=y
 CONFIG_SYS_MPC85XX_NO_RESETVEC=y
+CONFIG_USE_UBOOTPATH=y
 CONFIG_SYS_MONITOR_LEN=524288
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
@@ -39,6 +40,7 @@
 CONFIG_USE_BOOTFILE=y
 CONFIG_BOOTFILE="uImage"
 CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_USE_ROOTPATH=y
 CONFIG_SIMPLE_BUS_CORRECT_RANGE=y
 CONFIG_LBA48=y
 CONFIG_CHIP_SELECTS_PER_CTRL=0