supporting uImage

[DO1FJN]

I've written a similar ESP32 loader as part of a STM32 firmware.

For me a practical solutions was to wrap all bin files within uImage header+crc (I my case w/o compression). Because of my limited time I can't add this now.

A valid image can be easy generated like

mkimage -A xtensa -C none -T firmware -a 10000 -e 10000 -nFACTORY <ImageName> -d<BinaryImage.bin> <uImageName>

If no flash address is given, your esputil can check if a uImage header is present - no need to use a fixed file suffix.