add host-build for xtensa u-boot

target/config/Config.in.tools

@@ -81,6 +81,10 @@ config ADK_HOST_BUILD_U_BOOT_GIT
 	bool
 	default n
 
+config ADK_HOST_BUILD_U_BOOT_XTENSA
+	bool
+	default y if ADK_TARGET_ARCH_XTENSA
+
 config ADK_HOST_BUILD_PATCH
 	bool
 	default n