MLBEDSW-4812: Deep speech performance block config update

Deep speech was exhibiting poor performance in its first three
layers due to poor SHRAM utilisation.

 - Given a choice between multiple identical-cost block configs,
   the allocator was choosing the first one it encountered. This
   commit biases the choice towards blocks with a larger IFM
   fetch area to improve SHRAM utilisation.

Signed-off-by: Tim Hall <tim.hall@arm.com>
Change-Id: I2ff18a13444b8812cb451a606ff692bf290e7d20