[llvm] [AArch64] Split large loop dependence masks (PR #153187)

[Sam Tebbs via llvm-commits]

SamTebbs33 wrote:

Thanks Ben, I've incorporated your commits with a couple of changes (updated tests and removal of the `isLegalWhileWRorRWElementSize` function which I didn't think was necessary).

https://github.com/llvm/llvm-project/pull/153187