Compressed hints should be legal

[PeterRugg]

Flute currently bans the compressed hint encodings: at least C.NOP with nzimm != 0 and c.ADDI with nzimm == 0. I'm not sure if this is based on a past version of the spec that reserved these, but the current version seems pretty clear that they should be legal.

I believe deleting the following two lines would fix these cases, but I'm not sure if there are more:

Flute/src_Core/CPU/CPU_Decode_C.bsv

Line 770 in da86cb0

&& (nzimm6 != 0));

Flute/src_Core/CPU/CPU_Decode_C.bsv

Line 790 in da86cb0

&& (nzimm6 == 0));

[PeterRugg]

Yep, it's all the other hints too: see CTSRD-CHERI@d84f421