MLBEDSW-9142 Add support for fusing activation functions to chains

* Allow fusing multiple activations to chains as long as they are not
consecutive.
* Allow fusing of int16 Simoid and Tanh.
* Utilize all 8 LUT slots rather than reusing slot 0 every time.
* Extended live-range fusing to allow reusing IFM/OFM across opgroups.

Change-Id: Idce158551b23f4ea3824e662a045759d4e609a60
Signed-off-by: Jacob Bohlin <jacob.bohlin@arm.com>