The bits needed by striped loop restoration are now in
RestorationInfo (which also gets rid of a rather ugly extra
index).

The scratch buffer that's used for self-guided restoration has been
moved up to its own variable (rst_tmpbuf).

All the rest of the fields are now safely hidden inside restoration.c

This patch also does a big cleanup of the initialisation code in
loop_restoration_rows: it doesn't need to be as repetitive now that
the fields of YV12_BUFFER_CONFIG can be accessed by plane index.

Change-Id: Iba7edc0f94041fa053cdeb3d6cf35d84a05dbfaf