Use the common syntax of using ALIGNED_DECLARE to declare arrays

This was the only place where ALIGNED_DECLARE_MATRIX was used.
Use the ALIGNED_DECLARE macro instead of __align16
Remove the now unused macros __align16, ALIGNED_DECLARE_MATRIX_1D and ALIGNED_DECLARE_MATRIX_2D
Merge pull request #1037 from mstorsjo/unify-align-macros

Unify macros for alignment