Add an additional bootmenu option and commands to overwrite the GPT table with the custom one for upstream U-Boot. This is needed as the pre-installed GPT table differ and updating the GPT table is a requirement to install the upstream U-Boot (or the old U-Boot will be loaded) To make the migration to new U-Boot bootloader an user can now load the system with mtk_uartboot and select "Load GPT Table ..." in conjunction with other update command. Link: https://github.com/openwrt/openwrt/pull/18874 Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>