[llvm] [ARM][NEON] Add constraint to vld2 Odd/Even Pseudo instructions. (PR #79287)

[Alfie Richards via llvm-commits]

AlfieRichardsArm wrote:

@efriedma-quic Ah yes I think I see your point. My view was that `$dst` value in both was where the insertion is happening and the `$src` register is only there to facilitate for the Odd and Even instructions to use the same destination range. 

But it is more natural to view it as `VLDQQPseudoConstrained` has `$src` input which then sets the `$dst` output? 

So in this understanding a name such as `VLDQQPseudoInputDST` may be better?

https://github.com/llvm/llvm-project/pull/79287