linkage.h: move from blackfin to common includes

1. Add linkage.h support from blackfin to common include,
   which is a reduced version from Linux.
2. Add architecture part support of linkage.h into blackfin
3. Fix include path of in blackfin related to linkage.h
   due to header file movement.

Signed-off-by: Macpaul Lin <macpaul@andestech.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>