Vector part select

A 32-bit word contains four bytes (bits 31..24, 23..16, 15..8, 7..0). Build a circuit that reverses the byte order — useful when converting between little- and big-endian data.

AaaaaaaaBbbbbbbbCcccccccDddddddd  =>  DdddddddCcccccccBbbbbbbbAaaaaaaa