Replacig simm und uimm with offset

[christian-herber-nxp]

Issue stated to replace simm. I suspect we also want to replace uimm with offset.
Similar to other issues, this notion was taken from Zcb.
It may make sense to update there as well.

[tovine]

Aren't we missing information here (or making it less obvious) by removing the u and s variants in favor of just offset?
From an implementor's perspective it's immediately clear how the immediate bits need to be extended like it was written before, but when it just says offset then it takes more than just a quick glance at the encoding table to see what it should be.

I respect if this is the ARC's position on the matter, just wanted to raise the question.

EDIT: I see it's just in the mnemonic, and agree that it doesn't really matter that much there plus it looks better this way.