Merge branch '2022-05-04-spl-use-common-function-for-loading-and-parsing-images'

To quote the author:

This series adds support for loading all image types (Legacy, FIT (with
and without LOAD_FIT_FULL), and i.MX) to the MMC, SPI, NOR, NET, FAT,
and EXT load methods. It does this by introducing a helper function
which handles the minutiae of invoking the proper parsing function, and
reading the rest of the image.

Hopefully, this will make it easier for load methods to support all
image types that U-Boot supports, without having undocumented
unsupported image types. I applied this to several loaders which were
invoking spl_load_simple_fit and/or spl_parse_image_header, but I did
not use it with others (e.g. DFU/RAM) which had complications in the
mix.