Add mtd-utils package

[nuess0r]

The mtd-utils package contains the flashcp command that is needed to backup the SPI NOR Flash and write newer u-boot and SPL versions to it.

If your yocto image would contain mtd-utils if possible by default, it would make it for beginners a lot easier to start with the Star64, upgrade the SPI Flash and then install their preferred mainline kernel based distribution without having to set up a tftp server and going through u-boot commands.