Merge tag 'efi-2021-04-rc2-2' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for UEFI sub-system for efi-2021-04-rc2-2

Bug fixes:
* fix stack smashing in UEFI capsule updates
* correct loading of UEFI binaries where Virtual size is not a
  multiple of FileAlignment
* simplify detection of capsule files.
* buildman: use threading.is_alive() instead of removed method IsAlive()