Gate interintra using first partition pass stats

Added a speed feature to evaluate interintra motion mode based
on the stats collected during first partition search pass for speed 3

For speed 3 preset, BD-rate drop is seen by 0.02% (as per AWCY runs)
with encode time reduction of 1.5% (averaged across multiple test cases)

STATS_CHANGED

Change-Id: I648897e987eecb15c196ecb9833096b6009ec95c
diff --git a/av1/encoder/block.h b/av1/encoder/block.h
index 2458698..2d4f558 100644
--- a/av1/encoder/block.h
+++ b/av1/encoder/block.h
@@ -176,6 +176,8 @@
   uint8_t ref0_counts[REF_FRAMES];  // Counters for ref_frame[0].
   uint8_t ref1_counts[REF_FRAMES];  // Counters for ref_frame[1].
   int sample_counts;                // Number of samples collected.
+  uint8_t interintra_motion_mode_count[REF_FRAMES];  // Counter for interintra
+                                                     // motion mode
 } FIRST_PARTITION_PASS_STATS;
 
 #define MAX_INTERP_FILTER_STATS 64