[SLP][AArch64] Incorrectly estimated intrinsic as a function call.

We incorrectly assume intrinsic as a function call and it prevents us from
the opportunity to vectorize. On Aarch64 Cortex-A53 we think that
llvm.fmuladd.f64 is a function call which is wrong.

Differential Revision: https://reviews.llvm.org/D140392