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/P2041RDB.h b/include/configs/P2041RDB.h
index 707157e..0f0cdb3 100644
--- a/include/configs/P2041RDB.h
+++ b/include/configs/P2041RDB.h
@@ -306,8 +306,6 @@
 /*
  * Environment Configuration
  */
-#define CONFIG_ROOTPATH		"/opt/nfsroot"
-#define CONFIG_UBOOTPATH	u-boot.bin
 
 #define __USB_PHY_TYPE	utmi
 
@@ -315,7 +313,7 @@
 	"hwconfig=fsl_ddr:ctlr_intlv=cacheline,"		\
 	"bank_intlv=cs0_cs1\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 && "			\