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/P2041RDB_defconfig b/configs/P2041RDB_defconfig
index aea0b89..306432e 100644
--- a/configs/P2041RDB_defconfig
+++ b/configs/P2041RDB_defconfig
@@ -16,6 +16,7 @@
 CONFIG_ENABLE_36BIT_PHYS=y
 CONFIG_SYS_BOOK3E_HV=y
 CONFIG_SYS_CACHE_STASHING=y
+CONFIG_USE_UBOOTPATH=y
 CONFIG_PCIE1=y
 CONFIG_PCIE2=y
 CONFIG_PCIE3=y
@@ -57,6 +58,7 @@
 CONFIG_BOOTFILE="uImage"
 CONFIG_USE_ETHPRIME=y
 CONFIG_ETHPRIME="FM1@DTSEC1"
+CONFIG_USE_ROOTPATH=y
 CONFIG_FSL_SATA_V2=y
 CONFIG_SYS_SATA_MAX_DEVICE=2
 CONFIG_FSL_CAAM=y