Remove sysdeps/mips soft-fp subdirectories.

Remove sysdeps/mips soft-fp subdirectories.

As noted in
<https://sourceware.org/ml/libc-alpha/2014-10/msg00369.html>, soft-fp
sysdeps subdirectories (and more generally, subdirectories where
sysdeps/foo/Implies contains foo/bar) are unnecessary and should be
eliminated.  This patch does so for MIPS.

Tested for MIPS64 (all three ABIs, soft-float) that installed stripped
shared libraries are unchanged by this patch.

	* sysdeps/mips/soft-fp/sfp-machine.h: Move to ....
	* sysdeps/mips/mips32/sfp-machine.h: ... here.
	* sysdeps/mips/mips64/soft-fp/Makefile: Move to ....
	* sysdeps/mips/mips64/Makefile: ... here.
	* sysdeps/mips/mips64/soft-fp/e_sqrtl.c: Move to ....
	* sysdeps/mips/mips64/e_sqrtl.c: ... here.
	* sysdeps/mips/mips64/soft-fp/sfp-machine.h: Move to ....
	* sysdeps/mips/mips64/sfp-machine.h: ... here.
	* sysdeps/mips/mips32/Implies: Remove mips/soft-fp.
	* sysdeps/mips/mips64/n32/Implies: Remove mips/mips64/soft-fp.
	* sysdeps/mips/mips64/n64/Implies: Likewise.