regression 1029 (thread local storage): accept TEE_ERROR_NOT_SUPPORTED

The Thread Local Storage test (__thread attribute) is modified to accept
TEE_ERROR_NOT_SUPPORTED without failing. This return value will be used
in a later commit in case an unsupported compiler is used to build the
TA.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>