SM3 example code

[ben-marshall]

• Implement a baseline RV32/RV64 version of SM3
• Implement an accelerated version of SM3 using the proposed instructions.

[mjosaarinen]

You're free to use the quantitive SM3 code I wrote in March. SM3 doesn't seem to benefit much (at all?) from RV64 -- there's only one hash size. The breakup of the functions matches that I used for SHA2 and SHA3 in the https://github.com/mjosaarinen/lwsha_isa/ repo.

• sm3_rv32_cf.c: https://github.com/mjosaarinen/lwsha_isa/blob/master/sm3_rv32_cf.c The compression function is the main optimization target. The "instructions" are emulated by functions sm3_p0() and sm3_p1 defined on the top of the file. Additionally, it uses bitmanip stuff, emulated by functions defined in bitmanip.h and bitmanip.c
• sm3_wrap.c: https://github.com/mjosaarinen/lwsha_isa/blob/master/sm3_wrap.c with prototypes at sm3_wrap.h contains a single-call interface to the hash function that implements padding etc.
• sm3_test.c: https://github.com/mjosaarinen/lwsha_isa/blob/master/sm3_test.c contains very limited testing for the function with two test vectors from the standard text itself.