[llvm] [AArch64] Use vecshiftL64 instead of vecshiftR64 to match scalar SLI imm. (PR #139904)

[Ricardo Jesus via llvm-commits]

rj-jesus wrote:

> @rj-jesus Do you mind having this backported to the release branch?

Of course, I will do so just now.

https://github.com/llvm/llvm-project/pull/139904