Merge tag 'efi-2019-07-rc2-2' of git://git.denx.de/u-boot-efi

Pull request for UEFI sub-system for v2019.07-rc2 (2)

Fix a bunch of errors in the UEFI sub-system:

* implement missing UnloadImage(),
* implement missing RegisterProtocolNotify(),
* unload images in Exit(),
* parameter checks.

Provide a unit test for UnloadImage().
Remove a redundant function for unit tests.
Clean up the UEFI sub-system initialization