Instruction Modification: xc.msll.i, xc.msrl.i shift amount

[ben-marshall]

Increase the width of the cmshamt field from 4-bits to 6-bits, allowing full 64 bit immediate shifts.

• [x] xc.msll.i
• [x] xc.msrl.i
• [x] Binutils
• [x] Verification / formal checks

[ben-marshall]

This will change the encodings of xc.msll* and xc.msrl*, and thus require a re-build of binutils and all example software.