Values now carried over frame to frame.
Change to algorithm for decreasing threshold after
a hit and to max threshold (now based on speed)
Removed some old commented out code relating to
VP8 adaptive thresholds.
The impact of these changes tested on Akiyo (50 frames)
and measured in terms of unit rd hits is as follows:
Speed 0 84.36 -> 84.67
Speed 1 29.48 -> 22.22
Speed 2 11.76 -> 8.21
Speed 3 12.32 -> 7.21
Encode speed impact is broadly in line with these.
Change-Id: I5b886efee3077a11553fa950d796fd6d00c8cb19
aa5b67add0