[Attributor] Set floating point loads and stores as nofree in AANoFreeFloating

Summary:
The current implementation of AANoFreeFloating will incorrectly list floating
point loads and stores as may-free. This prevents other attributor instances
like HeapToStack from pushing some allocations to the stack.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D103975