Merge tag 'efi-2021-01-rc4' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for UEFI sub-system for efi-2021-01-rc4

* Provide a tool to create a file with UEFI variables to preseed UEFI
  variable store.
* Make size of UEFI variable store configurable.
* Add man pages for commands 'bootefi' and 'button'.