MLBEDSW-6645: MLCE: Optimize SRAM usage

- When compiling for shared SRAM the old scheduler has an option so
that it produces less SRAM than what the new scheduler manages to
produce. The old scheduler was able to creates more/longer cascades.

In order to improve the new scheduler, the following has been
implemented:

- Take persistent IFM's into account when creating the min schedule.
- Choose longer cascades when it is possible to reduce the total
SRAM usage compared to using shorter cascades.
- Updated calculation for estimated SRAM usage for elementwise ops.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: I209bbf2d94425e4f6aacb1d151b3b2aa65c0870b