MLBEDSW-6347: Improved fast storage allocator

- The fast storage allocator only looked at tensor size, giving priority
to larger tensors. The problem with this method is that it does not
consider the actual read/write access of the tensor. So, a smaller
tensor size can cause higher memory transactions than a bigger one.
- The solution is to calculate the read/write access of the tensor and
add that score to the decision when deciding where to place the tensors.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: I59eb9bd3a44a0238b576cfd8f09ff27012b99070