sparc: refactor cpu_relax to C

	* sysdeps/sparc/sparc64/cpu_relax.c: New file.
	* sysdeps/sparc/sparc32/sparcv9/cpu_relax.c: Likewise.
	* sysdeps/sparc/sparc64/cpu_relax.S: Remove file.
	* sysdeps/sparc/sparc32/sparcv9/cpu_relax.S: Likewise.

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