x86-64: Add logf with FMA

For workload-spec2017.wrf, on Skylake, it improves performance by:

                           Before            After     Improvement
reciprocal-throughput      16.1534          13.8874       16%
latency                    41.9642          34.3072       22%

	* sysdeps/x86_64/fpu/multiarch/Makefile (libm-sysdep_routines):
	Add e_logf-fma.
	(CFLAGS-e_logf-fma.c): New.
	* sysdeps/x86_64/fpu/multiarch/e_logf-fma.c: New file.
	* sysdeps/x86_64/fpu/multiarch/e_logf.c: Likewise.