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>