Add tags to all instructions which are extensions

[ThinkOpenly]

Many extensions include discriminators which clearly tag instructions which are included in the extension:

mapping clause encdec = RISCV_FMINM_S(rs2, rs1, rd)     if haveZfa()

(Note that issue #4 suggests a more robust tagging method.)

Not all extensions are well-tagged, however, especially if they are ratified and included in the "base ISA":

/* This file specifies the compressed instructions in the 'C' extension. */
[...]
mapping clause encdec_compressed = C_LW(ui6 @ ui53 @ ui2, rs1, rd)

It would be useful to include tags for these instructions as well, hopefully in a robust way as suggested in issue #4.

[AbhinavMir]

I think this can be closed since Sanket seems to have implemented this?

[ThinkOpenly]

I'd like see an audit performed that shows this is reasonably complete and accurate.

[ThinkOpenly]

Our upstream PR for this work riscv#506 has been merged! 🎉 Thanks for everyone's efforts on this!

Closing this issue...