Remove sysdeps/aarch64/soft-fp directory.

As per <https://sourceware.org/ml/libc-alpha/2014-10/msg00369.html>,
there should not be separate sysdeps/<arch>/soft-fp directories when
those are used by all configurations that use sysdeps/<arch>, and,
more generally, should not be sysdeps/foo/Implies files pointing to a
subdirectory foo/bar.  This patch eliminates the
sysdeps/aarch64/soft-fp directory accordingly, merging its contents
into sysdeps/aarch64.

Tested with build-many-glibcs.py that installed stripped shared
libraries for aarch64 configurations are unchanged by this patch.

	* sysdeps/aarch64/Implies: Remove aarch64/soft-fp.
	* sysdeps/aarch64/Makefile [$(subdir) = math] (CPPFLAGS): Add
	-I../soft-fp.  Moved from ....
	* sysdeps/aarch64/soft-fp/Makefile: ... here.  Remove file.
	* sysdeps/aarch64/soft-fp/e_sqrtl.c: Move to ....
	* sysdeps/aarch64/e_sqrtl.c: ... here.
	* sysdeps/aarch64/soft-fp/sfp-machine.h: Move to ....
	* sysdeps/aarch64/sfp-machine.h: ... here.