Add kcheck option for checking < X MB boot.img size
Some devices have a boot.img restriction size due to bootloader / partition size. For example, some `tegra` or `espresso` devices have a restriction of < 8 MB boot.img file size.
It could be a great option to check for < 7, 7.5, 8,... boot.img file size, according to each device, if there's any.
issue