[llvm] [AArch64][GISel] Assign registers into FPR if they feed into FP instructions indirectly via PHI (PR #94618)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Thanks. A test please. Do you really need the flag. The `TargetOpcode` of a MI could change between the IRTranslator and RBS. Then `DefinesFP` might be  misleading.

https://github.com/llvm/llvm-project/pull/94618