scalar-crypto: Add opcodes for RV32K, RV64K

- Adds opcodes for RV32 and RV64 scalar crypto.

- opcodes-rvk contains encodings which are for RV32 and RV64 base ISAs

- opcodes-rv32/64k contains encodings which are for RV32 or RV64

- parse_opcodes has been modified:

  - Wnable instructions to be listed as either RV32 or RV64 only, allowing
    these opcodes to overlap.

  - The C backend has been modifed to emit the "DECLARE_RV32_ONLY" or
    "DECLARE_RV64_ONLY" macros as needed.

  - The other backends have not been modified, and may need to be in the
    future.

 On branch scalar-crypto
 Changes to be committed:
	modified:   Makefile
	new file:   opcodes-rv32k
	new file:   opcodes-rv64k
	new file:   opcodes-rvk
	modified:   parse_opcodes