add json lib

buildroot-external/configs/ark1668e_devb_emmc_defconfig

@@ -26,6 +26,7 @@ BR2_PACKAGE_QT5BASE_FONTCONFIG=y
 BR2_PACKAGE_QT5BASE_JPEG=y
 BR2_PACKAGE_QT5BASE_PNG=y
 BR2_PACKAGE_QT5BASE_DBUS=y
+BR2_PACKAGE_QJSON=y
 BR2_PACKAGE_DBUS_CPP=y
 BR2_PACKAGE_FDK_AAC=y
 BR2_PACKAGE_LIBMAD=y