tee: optee: add const to tee_driver_ops and tee_desc structures

Add const to tee_desc structures as they are only passed as an argument
to the function tee_device_alloc. This argument is of type const, so
declare these structures as const too.
Add const to tee_driver_ops structures as they are only stored in the
ops field of a tee_desc structure. This field is of type const, so
declare these structure types as const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>