MLBEDSW-6430: MLCE: Vela splitting network into two ethos operators

- Due to how the graph is traversed, the final pass list contained unnecessary
multiple Ethos-U operators. Functionality wise not a problem but it adds extra
context switching between CPU and NPU.
- By applying sorting rules to the pass list, it is possible to create a more
optimal pass list that reduces the numbers of Ethos-U operator.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: Ib556f902e1f321b5c50238fada7aa92b9810b27a