RTL: Re-vamped crypto functional unit.

- Re-written instruction RTL and built "dropin" example FU.

- Parameterised for RV32/64 and whether different instructions are
  included or not.

- Formal checkers for lut4 and aes. Others TBD.

 On branch master
 Your branch is up-to-date with 'origin/master'.

 Changes to be committed:
	modified:   README.md
	modified:   rtl/Makefile
	modified:   rtl/README.md
	new file:   rtl/crypto-fu/Makefile.in
	new file:   rtl/crypto-fu/riscv_crypto_fu.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_aes_mix_columns.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_lut4.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_saes32.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_saes64.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_sboxes.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_sm3.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_ssha256.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_ssha512.v
	new file:   rtl/crypto-fu/riscv_crypto_fu_ssm4.v
	new file:   rtl/crypto-fu/tb_checker_lut4_rv32.v
	new file:   rtl/crypto-fu/tb_checker_saes.vh
	new file:   rtl/crypto-fu/tb_checker_saes32.v
	new file:   rtl/crypto-fu/tb_checker_saes64.v
	new file:   rtl/crypto-fu/tb_riscv_crypto_fu.v
	new file:   rtl/crypto-fu/verify.sby

 Changes not staged for commit:
	modified:   extern/riscv-gnu-toolchain (modified content)
	modified:   extern/riscv-isa-sim (modified content)