m68k: replace gcc specific macros with ones from compiler.h

m68k: replace gcc specific macros with ones from compiler.h

There is <linux/compiler.h> which provides macros for various gcc
specific constructs.  Eg: __weak for __attribute__((weak)).  I've
cleaned all instances of gcc specific attributes with the right macros
for all files under /arch/m68k

Link: http://lkml.kernel.org/r/1485540901-1988-3-git-send-email-gidisrael@gmail.com
Signed-off-by: Gideon Israel Dsouza <gidisrael@gmail.com>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>