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/am3517_evm_defconfig b/configs/am3517_evm_defconfig
index 6dd04a4..1e0baeb 100644
--- a/configs/am3517_evm_defconfig
+++ b/configs/am3517_evm_defconfig
@@ -33,6 +33,7 @@
 CONFIG_CMD_NAND=y
 # CONFIG_CMD_SPI is not set
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_CACHE=y
 # CONFIG_CMD_TIME is not set
 CONFIG_CMD_MTDPARTS=y