Convert CONFIG_BOOTP_SERVERIP to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTP_SERVERIP

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/adp-ag101p_defconfig b/configs/adp-ag101p_defconfig
index 503f2ae..49108ec 100644
--- a/configs/adp-ag101p_defconfig
+++ b/configs/adp-ag101p_defconfig
@@ -29,6 +29,7 @@
 CONFIG_ENV_ADDR=0x80140000
 CONFIG_BOOTP_SEND_HOSTNAME=y
 CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_BOOTP_SERVERIP=y
 CONFIG_DM=y
 CONFIG_MMC=y
 CONFIG_FTSDC010=y