Rename Zcmlsd to Zclsd

[aswaterman]

The other Zcm extensions prefix their mnemonics with cm.. To maintain consistency, we have two choices:

• Rename the extension to Zclsd and retain the instruction names
• Retain the extension name and rename the instructions

The ARC recommends the first option, because we think it is less confusing to keep the names the same between RV32 and RV64, just as Zilsd does.

(The argument in favor of the second option is that Zcm has traditionally been used as the prefix for instructions that conflict with Zcf/Zcd, but we think this consideration is somewhat less important.)