Add support for the following instructions:
- MUL (indexed and unpredicated vectors forms)
- SQDMULH (indexed and unpredicated vectors forms)
- SQRDMULH (indexed and unpredicated vectors forms)
- SMULH (unpredicated, predicated form added in SVE)
- UMULH (unpredicated, predicated form added in SVE)
- PMUL (unpredicated)
The specification can be found here:
https://developer.arm.com/docs/ddi0602/latest
Nitpick: Add a test with all registers .b (ditto for sqdmulh and sqrdmulh).