tee: Add some helpers to reduce boilerplate for tee client drivers

tee: Add some helpers to reduce boilerplate for tee client drivers

Similar to platform drivers (and others) create dedicated register and
unregister functions and a macro to simplify modules that only need to
handle driver registration in their init and exit handlers.

Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>