Drop the exporting of empty <linux/byteorder/generic.h>

Fix up the contents of <linux/byteorder/> so that it doesn't export a
content-free generic.h to user space.  This involves:

* Removing the __KERNEL__ tests from generic.h and dropping it from
  Kbuild.
* Wrapping the inclusions of generic.h in both big_endian.h and
  little_endian.h in __KERNEL__ tests.
* Shifting big_endian.h and little_endian.h from header-y to
  unifdef-y in Kbuild.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/byteorder/little_endian.h b/include/linux/byteorder/little_endian.h
index 86e62b7..05dc7c3 100644
--- a/include/linux/byteorder/little_endian.h
+++ b/include/linux/byteorder/little_endian.h
@@ -101,6 +101,8 @@
 #define __cpu_to_be16s(x) __swab16s((x))
 #define __be16_to_cpus(x) __swab16s((x))
 
+#ifdef __KERNEL__
 #include <linux/byteorder/generic.h>
+#endif
 
 #endif /* _LINUX_BYTEORDER_LITTLE_ENDIAN_H */