MIPS64r6 Assembler Tests

Assembler tests for:

- SQRT.fmt    - ABS.fmt     - ROUND.L.fmt - ROUND.W.fmt
- CEIL.L.fmt  - CEIL.W.fmt  - FLOOR.L.fmt - FLOOR.W.fmt
- SEL.fmt     - RINT.fmt    - CLASS.fmt   - MIN.fmt
- MAX.fmt     - cvt.d.l     - BITSWAP     - DBITSWAP
- DSBH        - DSHD        - WSBH        - ROTR
- SELEQZ      - SELNEZ      - CLZ         - CLO
- DCLZ        - DCLO        - SC          - SCD
- LL          - LLD

These are the assembler instructions which were added to support
intrinsic functions on MIPS64. Tests for additional assembler
instructions will follow.

Support added to the testing infrastructure for:

- Assembler instructions which use three registers; previously
  instructions were limited to one, or two, registers.
- Immediate values which have their sizes specified by the number of
  bits required to store them rather than the number of bytes, in both
  signed and unsigned versions.

Change-Id: I38c07dcbf2539825b25bed13aac05a26fa594b0b