x86: allow {store} to select alternative {,}PEXTRW encoding

x86: allow {store} to select alternative {,}PEXTRW encoding

The 0F C5 encoding is indeed a load type one (just that memory operands
are not permitted), while the 0F 3A 15 encoding is obviously a store.
Allow the pseudo prefixes to be used to select between them.

Also move (without any change) the secondary AVX512BW templates next to
the primary one.