This reverts commit 0859ac5866a0228f5607dd329f83f4a9622dedcc.

This caused a couple test failures, likely due to a mid-air collision.
Reverting for now to get the tree back to green and allow the original
author to run UTC/friends and verify the output.

This maybe a bug which is introduced by commit
6749ae36b4a33769e7a77cf812d7cd0a908ae3b9, and has been present ever
since.
In this case, `OtherReg` always overlaps with `DstReg` cause they from
the `Copy` all.

This works fine on main, but broke after a future patch.

PR causes build failures with expensive checks enabled

Reverts llvm/llvm-project#168546

Fix a problem exposed by #166483 using AV classes in more places.
`isVectorRegister` only accepts registers of VGPR or AGPR classes.
`hasVectorRegisters` additionally accepts the combined AV classes.

Fixes: #168761

Use the default, which freely coalesces anything it can.
This mostly shows improvements, with a handful of regressions.
The main concern would be if introducing wider registers is more
likely to push the register usage up to the next occupancy tier.

This patch enables the multi-group xnack replay mode by
configuring the hardware MODE register at kernel entry.
This aligns the hardware behavior with the compiler's
existing multi-group s_wait_xcnt insertion logic.

We previously got a duplicate implicit $exec operand. It didn't really
hurt anything (other than being a slight drag on compile-time
performance). Still, let's keep things clean.