64-bit instructions are split into two 32-bit words, the prefix and the
suffix. The prefix always comes before the suffix in PC order.
-| 0:5 | 6:31 | 0:31 |
+| 0:5 | 6:31 | 32:63 |
|--------|--------------|--------------|
-| EXT01 | v3.1 Prefix | v3.1 Suffix |
+| EXT01 | v3.1 Prefix | v3.0/1 Suffix |
svp64 fits into the "reserved" portions of the v3.1 prefix, making it possible for svp64, v3.0B (or v3.1 including 64 bit prefixed) instructions to co-exist in the same binary without conflict.