rt_instr: Pass the parent function name all the way down to the output message

As we are using common functions for performing the various
test-cases, we cannot use __func__ directly in those functions.  To
differentiate the test-cases in the final output, we need the name of
test to be passed all the way down to the output function.

Change-Id: Ia0c3dabeddf2e25b4aa395103c5261575ad6cac6
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>