efi_selftest: provide an EFI selftest application

A testing framework for the EFI API is provided.
It can be executed with the 'bootefi selftest' command.

It is coded in a way that at a later stage we may turn it
into a standalone EFI application. The current build system
does not allow this yet.

All tests use a driver model and are run in three phases:
setup, execute, teardown.

A test may be setup and executed at boottime,
it may be setup at boottime and executed at runtime,
or it may be setup and executed at runtime.

After executing all tests the system is reset.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>