byteorder: make swab.h include asm/swab.h like a regular header

Add swab.h to kbuild.asm and remove the individual entries from
each arch, mark as unifdef as some arches have some kernel-only
bits inside.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/asm-generic/Kbuild.asm b/include/asm-generic/Kbuild.asm
index 1870d5e..70d1855 100644
--- a/include/asm-generic/Kbuild.asm
+++ b/include/asm-generic/Kbuild.asm
@@ -31,6 +31,7 @@
 unifdef-y += sockios.h
 unifdef-y += stat.h
 unifdef-y += statfs.h
+unifdef-y += swab.h
 unifdef-y += termbits.h
 unifdef-y += termios.h
 unifdef-y += types.h