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/stm32mp15_basic_defconfig b/configs/stm32mp15_basic_defconfig
index 86ebbef..2d4b7cb 100644
--- a/configs/stm32mp15_basic_defconfig
+++ b/configs/stm32mp15_basic_defconfig
@@ -94,6 +94,8 @@
 # CONFIG_SPL_ENV_IS_NOWHERE is not set
 # CONFIG_SPL_ENV_IS_IN_SPI_FLASH is not set
 CONFIG_TFTP_TSIZE=y
+CONFIG_USE_SERVERIP=y
+CONFIG_SERVERIP="192.168.1.1"
 CONFIG_STM32_ADC=y
 CONFIG_SET_DFU_ALT_INFO=y
 CONFIG_USB_FUNCTION_FASTBOOT=y