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/am335x_boneblack_vboot_defconfig b/configs/am335x_boneblack_vboot_defconfig
index 64c1c53..b161b3b 100644
--- a/configs/am335x_boneblack_vboot_defconfig
+++ b/configs/am335x_boneblack_vboot_defconfig
@@ -29,6 +29,7 @@
 CONFIG_CMD_SPL=y
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_DNS2=y
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="am335x-boneblack"
 CONFIG_ENV_IS_IN_MMC=y