avcodec/mips: Restructure as per avutil/mips/generic_macros_msa.h

This patch modifies H264 loopfilter, weighted & bi-weighted prediction MIPS-SIMD optimized code according to improved version of generic macros.
Also there are minor code alignment changes.

Overall, this patch is just upgrading the code with styling changes and will bring it in sync with MIPS-SIMD optimized latest codebase at our end.
Signed-off-by: Shivraj Patil <shivraj.patil@imgtec.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>