MLECO-5117: Improving auto-generation of test files

The tests expected all the data types across input and output tensors
to be same. These were also limited to 8-bit signed/unsigned values.
This patch make it possible to have the test vectors be of different
types while being able to get a generic (void) pointer to arrays from
the generated getter functions.

Change-Id: Id6d8b13803cd2f2ed66fee52eaed86af194b995d
Signed-off-by: Kshitij Sisodia <kshitij.sisodia@arm.com>