Add support for generating and flashing depthcharge images

Depthcharge is a stock bootloader on Chrome OS devices which accepts FIT images in a specific format on specific partitions. This MR adds support for generating and flashing these images with mkdepthcharge utility from https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/35202.

Since i need to pass dtb to mkdepthcharge, i also need to handle cases when dtbs are located in /boot/dtbs-something and copy from there dtb specified in $deviceinfo_dtb