checkpatch: add test for positional misuse of section specifiers like __initdata

As discussed recently on the arm [1] and lm-sensors [2] lists, it is
possible to use section markers on variables in a way which gcc doesn't
understand (or at least not the way the developer intended):

static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = {

does NOT put exynos4_plls in the .initdata section.  The __initdata marker
can be virtually anywhere on the line, EXCEPT right after "struct".  The
preferred location is before the "=" sign if there is one, or before the
trailing ";" otherwise.

[1] http://permalink.gmane.org/gmane.linux.ports.arm.kernel/258149
[2] http://lists.lm-sensors.org/pipermail/lm-sensors/2013-August/039836.html

So, update checkpatch to find these misuses and report an error when it's
immediately after struct or union, and a warning when it's otherwise not
immediately before the ; or =.

A similar patch was suggested by Andi Kleen
https://lkml.org/lkml/2013/8/5/648



Signed-off-by: Joe Perches <joe@perches.com>
Suggested-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>