Port switch to 9-bit rate cost to vp10.
Brings the following commits to vp10: 269428e3 Tie the bit cost scale to a define. d13385ce Switch to 9-bit rate cost constants built on a 256 probability denominator. ad43a738 Fix a signed overflow in vp9 motion cost. 1c9b0918 Fix some interger overflow errors fac947df Restore previous motion search bit-error scale. Change-Id: I598ba7ee7efcde18439c31dfa96b86cbf297a580