Changes the CONFIG_FAST_SGR=1 strategy to not use any
subsampling for the r=1 filter, but for the r=2 filter
sub-sample vertically but combine only by filtering
horizontally in the last stage for odd rows.

Coding efficiency loss sems quite minimal.

Change-Id: I5644ac400b387c37a2d278db7f6ad3ac0a6b5e93