Auto min and max partition size experiment.
Speed feature experiment to set an upper and lower partition size limit based on what has been seen in spatial neighbors. This seems to gives quite reasonable speed gains in local (10-15%) and when used with speed 0 the losses are small (0.25% derf, 0.35% stdhd). However, for now I am only enabling it on speed 1 as there may be clashes with the existing temporal partition selection in speed 2. Using a tighter min / max around the range derived from the neighbors increases speed further but at the cost of a bigger quality loss. However, I think this spatial method could be combined with data from either the last frame or a variance method (or both) to refine the range of minimum and maximum partition size. I.e. consider the min and max from spatial and temporal neighbors and the variance recommendation. Change-Id: I1b96bf8b84368d6aad0c7aa600fe141b4f07435f