Reduce max_partition_size for low resolutions at speed 5.

For speed 5 real-time mode, the selection of the partition size for
superblocks on the segment (aq-mode=3) uses the non-rd recursive
pick partition search, and can sometimes select 64x64.

For low resolutions, visually better to limit this to 32x32.

Change-Id: I69657a7ed8899f8b3cf8c9c318a2509c5c72c565

vp9/encoder/vp9_encodeframe.c

diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index dcddefc..7bccc82 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -3572,7 +3572,11 @@
         set_offsets(cpi, tile_info, x, mi_row, mi_col, BLOCK_64X64);
         if (cpi->oxcf.aq_mode == CYCLIC_REFRESH_AQ && cm->seg.enabled &&
             xd->mi[0]->mbmi.segment_id) {
-          x->max_partition_size = BLOCK_64X64;
+          // Use lower max_partition_size for low resoultions.
+          if (cm->width <= 352 && cm->height <= 288)
+            x->max_partition_size = BLOCK_32X32;
+          else
+            x->max_partition_size = BLOCK_64X64;
           x->min_partition_size = BLOCK_8X8;
           nonrd_pick_partition(cpi, td, tile_data, tp, mi_row, mi_col,
                                BLOCK_64X64, &dummy_rdc, 1,