Merge changes Ib9428dc9,Ide04717a,If1dba7d8,I6da97880 into nextgenv2

* changes:
  Merge rd_stats only when it is valid
  Let parentheses in handle_inter_mode be symmetric
  Add RD_STATS into MB_MODE_INFO
  Add txb_coeff_cost_map

diff --cc av1/common/blockd.h
Simple merge

diff --cc av1/encoder/bitstream.c
Simple merge

diff --cc av1/encoder/rdopt.c
Simple merge