Not complete, but enough for Shell.efi and SCT.efi.  We'll implement the
rest as needed or once we have SCT running properly so there is a way to
validate the interface against the conformance test suite.

Initial skeleton written by Leif, and then implementation by Rob.

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
[Fill initial skeleton]
Signed-off-by: Rob Clark <robdclark@gmail.com>
[Rebase on v2018.03-rc1]
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>