Properly support loopfiltering-across-tiles in combination with
superres and/or loop-restoration:

Upscale one tile column at a time, rather than doing the whole
frame at once. This allows us to correctly support the loop filter
across tiles flag, by temporarily extending the left/right boundaries
of each tile column to avoid sampling from adjacent tiles.

This code is also reused by striped-loop-restoration, when upscaling the
deblocked context above/below each stripe. That way, we i) ensure
that the upscaling is done consistently, and ii) fix the last remaining
case where loop-restoration didn't respect the loop filter across tiles
flag.

This also makes it easy to perform extension of the left/right edges
of the frame "as needed", so we don't need to extend the frame borders
immediately after deblocking. This should give marginally better CDEF
filtering for frames using superres.

Change-Id: I28712a177853a20c9eb2993e740da8ba7c95a8cc