[llvm] [AArch64] Use FMOVDr for clearing upper bits (PR #83107)

[David Green via llvm-commits]

davemgreen wrote:

Hi - No it should be defined in the architecture that is clears the upper bits of the register, so should be OK. Most of the instructions end up working that way so it is usually treated quite efficiently.

https://github.com/llvm/llvm-project/pull/83107