Merge tag 'doc-2021-04-rc1-2' of https://gitlab.denx.de/u-boot/custodians/u-boot-efi

Pull request for documentation tag doc-2021-04-rc1 (2)

* Man-pages for sbi, exit, for, echo, loady, true, false, conitrace
* Adjust suppression of newline in echo command.
* Provide unit test for echo command.