Refactor codes about motion search

1. Add "best_mv" in MACROBLOCK to store the best motion vector
during motion search, so that we don't need to pass its pointer
to various motion search functions.

2. Declare some functions as static when possible.

3. Fix some indents.

Change-Id: I0778146c0866cbc55e245988c59222577ea8260e
7 files changed