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/include/configs/T208xRDB.h b/include/configs/T208xRDB.h
index d8213b4..2a32fe3 100644
--- a/include/configs/T208xRDB.h
+++ b/include/configs/T208xRDB.h
@@ -385,8 +385,6 @@
 /*
  * Environment Configuration
  */
-#define CONFIG_ROOTPATH	 "/opt/nfsroot"
-#define CONFIG_UBOOTPATH "u-boot.bin"	/* U-Boot image on TFTP server */
 
 #define __USB_PHY_TYPE		utmi
 
@@ -396,7 +394,7 @@
 	"bank_intlv=auto;"					\
 	"usb1:dr_mode=host,phy_type=" __stringify(__USB_PHY_TYPE) "\0"\
 	"netdev=eth0\0"						\
-	"uboot=" __stringify(CONFIG_UBOOTPATH) "\0"		\
+	"uboot=" CONFIG_UBOOTPATH "\0"		\
 	"ubootaddr=" __stringify(CONFIG_TEXT_BASE) "\0"	\
 	"tftpflash=tftpboot $loadaddr $uboot && "		\
 	"protect off $ubootaddr +$filesize && "			\