checkpatch: only apply kconfig help checks for options which prompt

The intent of this check is to catch the options which the user will see
and ensure they are properly described.  It is also common for internal
only options to have a brief description.  Allow this form.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>