Use libm_alias_float for e500.

Continuing the preparation for additional _FloatN / _FloatNx function
aliases, this patch makes an e500 libm function implementation use
libm_alias_float to define function aliases.

Tested with build-many-glibcs.py that installed stripped shared
libraries are unchanged for its e500 configurations.

	* sysdeps/powerpc/powerpc32/e500/nofpu/s_fabsf.S: Include
	<libm-alias-float.h>.
	(fabsf): Define using libm_alias_float.