checkpatch: warn on missing spaces in broken up quoted

Checkpatch already complains when people break up quoted strings but
it's still pretty common.  One mistake that people often make is they
leave out the space character between the two strings.

This check adds around 450 new warnings and has a low rate of false
positives.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andy Whitcroft <apw@canonical.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>