Add a strict mode for auto_min_max_partition_size feature

In this new mode, the size range is strictly determined by the min
and max partition size in neighborhood blocks.

Niklas720 encoding time at cpu-used -5 goes from 56250ms to 50676ms,
a 10% reduction.

Change-Id: I316b0e2ac967ff3fad57b28d69c0ec80b7d8b34e