JIT: SVE Cleanup - Simplify handling of RMW intrinsics in LSRA

[TIHan]

Discussion: #104704 (comment)

BuildHWIntrinsic in lsraarm64.cpp is getting a little complicated, especially when it comes to handling RMW intrinsics and when ConditionalSelect wraps a RMW intrinsic.

The logic that handles the RMW intrinsics makes assumptions on which operand on the intrinsic is the RMW node based on flags. Instead, as mentioned in the discussion, we really just need to have a function that tells us which operand is the RMW node and then BuildHWIntrinsic will know how to handle it in a general way.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[a74nh]

priority:3 for RC1 snap : Not required, but it'd be nice to have for maintainability.