UPSTREAM: firmware: arm_ffa: Add support for SMCCC as transport to FFA driver

There are requests to keep the transport separate in order to allow
other possible transports like virtio. So let us keep the SMCCC transport
specific routines abstracted.

It is kept simple for now. Once we add another transport, we can develop
better abstraction.

Link: https://lore.kernel.org/r/20210521151033.181846-4-sudeep.holla@arm.com


Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
(cherry picked from commit 714be77e)
Change-Id: Ifcc53535ca4cf16a486634efac5cab4f31e82d1b
Bug: 168585974
Signed-off-by: Will Deacon <willdeacon@google.com>