Merge branch '2022-03-31-image-add-a-stage-pre-load' into next

To quote the author:
This series adds a stage pre-load before launching an image.  This stage
is used to read a header before the image and this header contains the
signature of the full image.  So u-boot may check the full image before
using any data of the image.

The support of this header is added to binman, and a command verify
checks the signature of a blob and set the u-boot env variable
"loadaddr_verified" to the beginning of the "real" image.

The support of this header is only added to binman, but it may also be
added to mkimage.