[llvm] [AArch64] Sink llvm.vscale.i32 into blocks for better isel (PR #93465)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

The patch looks reasonable but before accepting I would like to query why it's needed.  I would expect functions to be decorated with a vscale_range attribute (clang adds `vscale_range(1,16)` when targeting SVE) which allows instcombine to remove the zero-extend and just emit a call to vscale.i64.

https://github.com/llvm/llvm-project/pull/93465