Since include/linux/linkage.h includes <asm/linkage.h>, the basic
coding style we should follow is:

 - <linux/linkage.h> should contain default macro defines
 - <asm/linkage.h> can define arch-specific macros and override the
   default ones in <linux/linkage.h>

The arch/blackfin/include/asm/linkage.h has redundant defines that
are already defined in <linux/linkage.h>.
Replace it with the one imported from Linux 3.19-rc6.

Generally, <asm/linkage.h> should not be included directly.
Fix two files to include <linux/linkage.h> instead.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>