soft-fp: Condition sfp-machine.h include path on __KERNEL__.

soft-fp: Condition sfp-machine.h include path on __KERNEL__.

My Linux kernel patch to update the kernel to current glibc soft-fp
<https://sourceware.org/ml/libc-alpha/2015-02/msg00107.html> still
leaves a few small differences between the two copies of soft-fp.

I think it's desirable to avoid such differences completely if
possible by having one set of sources suitable for use in both places.
To that end, this patch introduces a conditional on __KERNEL__ for the
path by which sfp-machine.h is included.

Tested for powerpc-nofpu that installed stripped shared libraries are
unchanged by this patch.

	* soft-fp/soft-fp.h [!_LIBC && __KERNEL__]: Include
	<asm/sfp-machine.h> instead of <sfp-machine.h>.