Merge tag 'efi-2020-07-rc4-2' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Merge tag 'efi-2020-07-rc4-2' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for UEFI sub-system for efi-2020-07-rc4 (2)

The following problems are resolved:

* When booting via UEFI an SMBIOS table is presented to the operating
  system. If U-Boot tries to add an empty string, this results in corrupted
  SMBIOS information. We will now use "Unknown" as property value.
* The EFI_RNG_PROTOCOL uses the DM_RNG drivers. For the virtio RNG driver
  the missing DM_RNG Kconfig dependency is added.
* Missing function descriptions for the EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL are
  added.