tpm2: ftpm: add the device in the OP-TEE services list

commit fe8a4ed0 ("tee: optee: discover services dependent on tee-supplicant")
is trying to automatically scan and add TAs that are presented on pseudo
bus from the secure world.
In order to be able to list and compare the scanned devices the available drivers
have to register themselves on the op-tee service list.

Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>