Refactoring in preparation for OBMC optimizations.

- Use int32_t instead of int in vpx_obmc{variance,sad} functions
- Remove weigthed_src and obmc mask strides and assume contiguous
  buffers. These inputs can always be packed as contiguous arrays.

Change-Id: I74c09b3fb3337f13d39e13a9cb61e140536f345d
9 files changed