Handle sg input and output for Squeeze operator

Update to handle the case when the Squeeze Op ifm/ofm are the
subgraph ifm/ofm, to facilitate the removal of the Squeeze Op.
Adding NOP to maintain the original tensors.
Updated pytests for squeeze operator.

Signed-off-by: Jonas Ohlsson <jonas.ohlsson@arm.com>
Change-Id: I623cae05e696fb16ccf29dedc42fd822601e9fd9