MLBEDSW-6148: Allow overwrite of subgraph input

This change will allow the subgraph's input tensor
to be reused/overwritten by the output from an elementwise op
if there is only one consumer attached to the input tensor.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: I317188af11a5470614770e18dc8973462fd5f21c