Support mixed-precision input tensors for TOSA unit test.

Bring CONV2D/DEPTHWISE_CONV2D/TRANSPOSE_CONV2D/FULLY_CONNECTED up running.

Other minor fixes:
- reference model should bail out if shape is invalid, along with "goto done" cleanup.
- cleanup typos/duplicate in tosa_test_gen.py/tosa_serializer.py.
- wrong input_zp/output_zp being generated for RESCALE.

Signed-off-by: Kevin Cheng <kevin.cheng@arm.com>
Change-Id: Ic1f3fe0090482bdee8a61508be7c738714191e19