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

This patch modifies HEVC mc MIPS-SIMD optimized code according to improved version of generic macros.

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>