Merge branch '2023-08-29-integrate-efi-capsule-update-better-in-to-u-boot-buildflow...

To quote the author:
This patchset aims to bring two capsule related tasks under the U-Boot
build flow.

The first task is related to generation of capsules. The capsules can be
generated as part of U-Boot build, and this is being achieved through
binman, by adding a capsule entry type. The capsules can be generated by
specifying the capsule parameters as properties under the capsule entry
node.

The other task is the embedding of the public key into the platform's
DTB. The public key is in the form of an EFI Signature List(ESL) file
and is used for capsule authentication. This is being achieved by adding
the signature node containing the capsule public key in the platform's
DTB.

Corresponding changes have also been made to the test setup of the EFI
capsule update feature. The ESL public key file was embedded into the
sandbox platform's test.dtb as part of the test setup, post U-Boot
build. This is now no longer needed as the embedding of the ESL happens
as part of the build.

Secondly, the capsules needed for testing the EFI capsule update feature
were being generated through the invocation of the mkeficapsule tool.
This setup has also been changed to introduce generation of these
capsules through binman.

The document has been updated to reflect the above changes.