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/am57xx_hs_evm_usb_defconfig b/configs/am57xx_hs_evm_usb_defconfig
index 3b155cc..c21a875 100644
--- a/configs/am57xx_hs_evm_usb_defconfig
+++ b/configs/am57xx_hs_evm_usb_defconfig
@@ -47,6 +47,7 @@
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_AB_SELECT=y
+CONFIG_BOOTP_DNS2=y
 # CONFIG_CMD_PMIC is not set
 CONFIG_CMD_AVB=y
 CONFIG_OF_CONTROL=y