MLBEDSW-10624: MLCE: Fix MAC cycle calculation

Fix regression introduced by commit a3a1df53 that affected
Ethos-U85 performance estimations. The MAC count from EstimateConvCycles
was not properly captured, leading to zero MACs.

- Store MAC count from EstimateConvCycles in cycles.macs.
- Corrected the logic when to multiply total MACs by ifm depth

Change-Id: I3a927a613e752a98dc3cbfd639d478cffce805cd
Signed-off-by: Johan Alfvén <johan.alfven@arm.com>