tee: optee: system thread call property

Adds an argument to do_call_with_arg() handler to tell whether the call
is a system thread call or not. This change always sets this info to false
hence no functional change.

This change prepares management of system invocation proposed in a later
change.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Co-developed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>
[jw: clarified that it's system thread calls]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>