Speed up subpel search for USE_2_TAPS

In tpl module, bilinear filter is used for sub-pel search.
However, optimized functions were not used during sub-pel
search when subpel_search_type is USE_2_TAPS in
av1_find_best_sub_pixel_tree(). This patch fixes the same.

Encoder performance results averaged over all resolutions
are as follows:

      Instruction Count
cpu     Reduction(%)
 1        1.83
 2        1.84

This change is bit-exact for all presets.

Change-Id: I0d5a9cc53f0523972dce788324618568bb7975a6

av1/encoder/mcomp.c

diff --git a/av1/encoder/mcomp.c b/av1/encoder/mcomp.c
index b451a21..b89b12f 100644
--- a/av1/encoder/mcomp.c
+++ b/av1/encoder/mcomp.c
@@ -2895,7 +2895,7 @@
                             best_mv->col + diag_step.col };
   int has_better_mv = 0;
 
-  if (var_params->subpel_search_type != USE_2_TAPS_ORIG) {
+  if (var_params->subpel_search_type > USE_2_TAPS) {
     check_better(xd, cm, &row_bias_mv, best_mv, mv_limits, var_params,
                  mv_cost_params, besterr, sse1, distortion, &has_better_mv);
     check_better(xd, cm, &col_bias_mv, best_mv, mv_limits, var_params,
@@ -3326,7 +3326,7 @@
     *distortion = start_mv_stats->distortion;
     *sse1 = start_mv_stats->sse;
   } else {
-    if (subpel_search_type != USE_2_TAPS_ORIG) {
+    if (subpel_search_type > USE_2_TAPS) {
       besterr = upsampled_setup_center_error(xd, cm, bestmv, var_params,
                                              mv_cost_params, sse1, distortion);
     } else {
@@ -3346,7 +3346,7 @@
     }
 
     MV diag_step;
-    if (subpel_search_type != USE_2_TAPS_ORIG) {
+    if (subpel_search_type > USE_2_TAPS) {
       diag_step = first_level_check(xd, cm, iter_center_mv, bestmv, hstep,
                                     mv_limits, var_params, mv_cost_params,
                                     &besterr, sse1, distortion);