xen/lib: Switch to xen/byteorder.h

xen/lib: Switch to xen/byteorder.h

In divmod.c, additionally swap xen/lib.h for xen/macros.h as only ABS() is
needed.

In find-next-bit.c, ext2 has nothing to do with this logic.  It was a local
modification when the logic was imported from Linux, because Xen didn't have a
suitable helper at the time.

The new infrastructure does have a suitable primitive, so use it.

No functional change.

Signed-off-by: Lin Liu <lin.liu@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>