checkpatch: add a test for const with __read_mostly uses

checkpatch: add a test for const with __read_mostly uses

const objects shouldn't be __read_mostly.  They are read-only.

Marking these objects as __read_mostly causes section conflicts with LTO
linking.

So add a test to try to avoid this issue.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>