Change some macros to be more sensitive to memory alignment, thus avoiding

Change some macros to be more sensitive to memory alignment, thus avoiding
useless loads/stores and calculations of permutation vectors.
Affected functions are all of mc_luma, mc_chroma, 'get_ref', SATD, SA8D and deblock.
Gains globally vary from ~5% - 15% on a depending on settings running on a 1.42 ghz G4.