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/pepper_defconfig b/configs/pepper_defconfig
index 6585ac0..5d79d47 100644
--- a/configs/pepper_defconfig
+++ b/configs/pepper_defconfig
@@ -27,6 +27,7 @@
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SPI=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y