sparc: refactor sparc32 nearbyint{f} selector to C

This patch refactors the sparc32 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/sparc32/sparcv9/fpu/multiarch/Makefile
	(libm-sysdep_routines): Add s_nearbyintf-generic and
	s_nearbyint-generic.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyint-generic.S:
	New file.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyint.c: Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyintf-generic.S:
	Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyintf.c:
	Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyint.S: Remove
	file.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_nearbyintf.S:
	Likewise.

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