optee: OCALL support without Ocall specific SHM allocation

Enable OCALL support specifically for OP-TEE without support for
Ocall specific shared memory allocation.

This change it fully based on the OCALL implementation proposal from
Hernan Gatta posted in [1] with modifications to remove OCall specific
shared memory allocation.

Link: [1] linaro-swg/linux#72
Co-developed-by: Hernan Gatta <hegatta@microsoft.com>
Signed-off-by: Hernan Gatta <hegatta@microsoft.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Change-Id: I70e9a0c0730df96277a2f4c0619d844e26d125ec

Author: etienne-lms