Port switch to 9-bit rate cost to vp10.

Port switch to 9-bit rate cost to vp10.

Brings the following commits to vp10:
269428e Tie the bit cost scale to a define.
d13385c Switch to 9-bit rate cost constants built on a 256 probability denominator.
ad43a73 Fix a signed overflow in vp9 motion cost.
1c9b091 Fix some interger overflow errors
fac947d Restore previous motion search bit-error scale.

Change-Id: I598ba7ee7efcde18439c31dfa96b86cbf297a580