Merge tag 'efi-2020-07-rc1' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for UEFI sub-system for efi-2020-07-rc1

This pull request

* provides an implementation of UEFI secure booting
* fixes a problem with the rsa_mod_exp driver which stops some boards
  from booting when CONFIG_RSA is enabled which is needed for UEFI
  secure booting
* enables the EFI_RNG_PROTOCOL if DM_RNG is enabled
* fixes some function comments