Merge tag 'efi-2021-04-rc1' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Merge tag 'efi-2021-04-rc1' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for UEFI sub-system for efi-2021-04-rc1

In the UEFI sub-system:

* implement non-blocking file services
* print boot device and file path in helloworld.efi
* improve detection of boot device
* correct argument handling in efivar.py
* implement EFI_DT_FIXUP_PROTOCOL

Bug fixes:

* adjust conitrace command for low baud rates
* check that FIT images are valid FDTs