Convert CONFIG_BOOTP_DNS2 to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTP_DNS2
   CONFIG_BOOTP_PXE_CLIENTARCH

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/chiliboard_defconfig b/configs/chiliboard_defconfig
index afc73dc..01c11435 100644
--- a/configs/chiliboard_defconfig
+++ b/configs/chiliboard_defconfig
@@ -31,6 +31,7 @@
 CONFIG_CMD_NAND=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_CMD_MTDPARTS=y
 CONFIG_MTDIDS_DEFAULT="nand0=8000000.nand"