BACKPORT: dt/bindings: add bindings for optee

Introduces linaro prefix and adds bindings for ARM TrustZone based OP-TEE
implementation.

Change-Id: I8992ce7476d3cb232600f1691ef698f7403cdc62
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
(cherry picked from commit c8bfafb1594435889b571b79325011e8b7fd087b)
Signed-off-by: Victor Chong <victor.chong@linaro.org>