sparc: refactor sparc64 nearbyint{f} selector to C

sparc: refactor sparc64 nearbyint{f} selector to C

This patch refactors the sparc64 ifunc selector to a C implementation.
Also, the generic symbol is moved to its own implementation file
s_nearbyint{f}-generic.S).

Checked on sparc64-linux-gnu and sparcv9-linux-gnu.

	* sysdeps/sparc/sparc64/fpu/multiarch/Makefile
	(libm-sysdep_routines): Add s_nearbyint-generic and
	s_nearbyintf-generic objects.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyint-generic.S: New file.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyint.c: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyintf-generic.S: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyintf.c: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyint.S: Remove file.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_nearbyintf.S: Likewise.

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>