sharpness was not recalculated in vp8cx_pick_filter_level_fast

remove last_filter_type. all values are calculated, don't need to update
the lfi data when it changes.

always use cm->sharpness_level. the extra indirection was annoying.

don't track last frame_type or sharpness_level manually. frame type
only matters for motion search and sharpness_level is taken care of in
frame_init

move function declarations to their proper header

Change-Id: I7ef037bd4bf8cf5e37d2d36bd03b5e22a2ad91db