MLBEDSW-5384 FC layers run on NPU if underlying shape is 2D

*Added generic function which checks if underlying shape of
FullyConnected operation is 2D and performs shape reduction
*Fully connected operation >2 dimensions now run on NPU if the above
case is satisfied
*constraint_fc_output_2d and rewrite_fully_connected_input refactored
*Added unit test to confirm this functionality

Signed-off-by: Ayaan Masood <Ayaan.Masood@arm.com>
Change-Id: I0e29c767e5b84841eb53bbc44464b36a454f7b38