Refactor CommonTileParams from AV1_COMMON

Also, refactor local variables/args for tiles when we can.

BUG=aomedia:2610

Change-Id: Ia07cdfb5e9351c8099199caca71f1028e83a85ed
diff --git a/av1/encoder/segmentation.c b/av1/encoder/segmentation.c
index 43a2803..d2b0ab0 100644
--- a/av1/encoder/segmentation.c
+++ b/av1/encoder/segmentation.c
@@ -183,10 +183,10 @@
   // First of all generate stats regarding how well the last segment map
   // predicts this one
   if (!scale_up) {
-    for (tile_row = 0; tile_row < cm->tile_rows; tile_row++) {
+    for (tile_row = 0; tile_row < cm->tiles.rows; tile_row++) {
       TileInfo tile_info;
       av1_tile_set_row(&tile_info, cm, tile_row);
-      for (tile_col = 0; tile_col < cm->tile_cols; tile_col++) {
+      for (tile_col = 0; tile_col < cm->tiles.cols; tile_col++) {
         MB_MODE_INFO **mi_ptr;
         av1_tile_set_col(&tile_info, cm, tile_col);
         mi_ptr = cm->mi_grid_base + tile_info.mi_row_start * cm->mi_stride +