Cleanup sync_file_range implementation

Since GLIBC requires a minimum 2.6.32 kernel, the patch cleanups
the mips code to assume __NR_sync_file_range and the powerpc one
to either assume __NR_sync_file_range2 or __NR_sync_file_range.

Checked on powerpc64le and build for mips (ABIO32, ABIN32, and ABI64).

	* sysdeps/unix/sysv/linux/powerpc/powerpc64/sync_file_range.c
	(__NR_sync_file_range2): Assume it is always defined.
	* sysdeps/unix/sysv/linux/mips/mips32/sync_file_range.c
	(__NR_sync_file_range): Assume it is always defined.