efi_loader: Add headers for EDK2 StandAloneMM communication

In Arm devices OP-TEE has the ability to run StandAloneMM (from EDK2)
in a separate partition and handle UEFI variables.
A following patch introduces this functionality.

Add the headers needed for OP-TEE <--> StandAloneMM communication

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>