MdeModulePkg: introduce non-discoverable device protocol

Introduce a protocol that can be exposed by a platform for devices that
are not discoverable, usually because they are wired straight to the
memory bus rather than to an enumerable bus like PCI or USB.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Tested-by: Marcin Wojtas <mw@semihalf.com>