The end results should be essentially the same, except hopefully a
little better because the previous code got the costing slightly
wrong if there were multiple tiles.

The code was doing something quite complicated to search for the best
restoration types; this patch makes it much simpler. Basically,
av1_pick_filter_restoration loops over the planes in the image. For
each plane, it loops over the possible restoration types, calling
search_rest_type for each one.

search_rest_type iterates over the restoration units in the image,
resetting the current context on tile boundaries and calling
search_<rest_type> for each restoration unit.

The search_norestore function just computes the SSE error with no
restoration. The search_wiener and search_sgrproj functions compute
the best set of coefficients and then the resulting SSE error with
those coefficients (ignoring the bit cost, so the result can be
re-used for switchable restoration).

In all cases but search_norestore, the search function has to decide
what restoration type is best for each restoration unit. For example,
search_wiener could choose to enable or disable Wiener filtering on
this unit.

Eventually, search_rest_type calculates the RDCOST after summing bit
rates and SSE errors over the restoration units. This cost gets
returned to av1_pick_filter_restoration which can then choose the best
frame-level restoration type.

Change-Id: I9bc17eb47cc46413adae749a43a440825c41bba6