32-bit instructions require a prefix-marker bit, it does effectively
double the **entirety** of the 32-bit Major Opcode space.
+this "doubling" is already public and part of EXT001, the idea
+here is to mirror that (bit 6), but unlike EXT001, use bit 7
+to mark whether the instruction is SVP64-vector or SVP64-single.
+
| 0-5 | 6 | 7 | 8-31 | Description |
|-----|---|---|------|---------------------------|
| PO | 0 | 0 | nnnn | new, scalar (SVP64Single) |