sparc: refactor sparc64 rint{f} selector to C

sparc: refactor sparc64 rint{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_rint{f}-generic.S).

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

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

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