[X86] Fix fmul throughput/latency/uops counts

Matches numbers from AMD SoG + Agner - should always be on FPU Pipes 0+1, no additional uops for folded instructions and znver1 double pumps 256-bit vectors and is always latency = 4cy for f64 multiplies

Noticed while adding fmul CostKinds support to the x86 cost models in rG0735200e3f50 and znver1 wasn't being flagged as requiring 2uop for 256-bit vectors