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/am43xx_evm_rtconly_defconfig b/configs/am43xx_evm_rtconly_defconfig
index a0a6661..66fe744 100644
--- a/configs/am43xx_evm_rtconly_defconfig
+++ b/configs/am43xx_evm_rtconly_defconfig
@@ -23,6 +23,7 @@
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_NAND=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_MTDPARTS=y
 CONFIG_MTDIDS_DEFAULT="nand0=nand.0"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=nand.0:256k(NAND.SPL),256k(NAND.SPL.backup1),256k(NAND.SPL.backup2),256k(NAND.SPL.backup3),512k(NAND.u-boot-spl-os),1m(NAND.u-boot),256k(NAND.u-boot-env),256k(NAND.u-boot-env.backup1),7m(NAND.kernel),-(NAND.file-system)"