rc: compute average of qpaRc, qpAq per frame even in 2 pass
rc: calculate mvBits, coefBits per Cu for 2 pass in skip mode as well
entropy: do not code a scaling list in PPS

The scaling list in PPS is only necessary to override the scaling list in the
SPS.  We will only ever have at most one scaling list (at this time)
entropy: nits
entropy: remove ambiguity about timing info signaling
entropy: reorder methods in general encode order for clarity, no logic change