further improvements in split & merge; started using non-temporary store instructions...

further improvements in split & merge; started using non-temporary store instructions (#12063)

* 1. changed static const __m128/256 to const __m128/256 to avoid wierd instructions and calls inserted by compiler.
2. added universal intrinsics that wrap MOVNTPS and other such (non-temporary or "no cache" store) instructions. v_store_interleave() and v_store() got respective flags/overloaded variants
3. rewrote split & merge to use the "no cache" store instructions. It resulted in dramatic performance improvement when processing big arrays

* hopefully, fixed some test failures where 4-channel v_store_interleave() is used

* added missing implementation of the new universal intrinsics (v_store_aligned_nocache() etc.)

* fixed silly typo in the new intrinsics in intrin_vsx.hpp

* still trying to fix VSX compiler errors

* still trying to fix VSX compiler errors

* still trying to fix VSX compiler errors

* still trying to fix VSX compiler errors