Merge tag 'efi-2022-04-rc3-2' of https://source.denx.de/u-boot/custodians/u-boot-efi

Pull request for efi-2022-04-rc3-2

Documentation:
* Fix description for SiFive Unmatched
* Add libgnutls28-dev to build dependencies

UEFI
* Avoid possibly invalid GUID pointers for protocol interfaces

Other
* Serial console support for cls command