[AMDGPU] Added isCommutable attribute to V_ADD_NC_U16

[easyonaadit]

Some VOP3 instructions are commutable, but have not been
defined as such, hence they are not merged by Machine-cse.
The isCommutable attribute has been added to them now.
For swapping operands in an instruction, there was no support
if both operands were literals, I have added support for swapping
two literals as well. (SIInstrInfo.cpp: commuteInstructionImpl)

This fixes #111205.

[github-actions]

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