kcsan: Clean up the main KCSAN Kconfig option

This patch cleans up the rules of the 'KCSAN' Kconfig option by:

  1. implicitly selecting 'STACKTRACE' instead of depending on it;
  2. depending on DEBUG_KERNEL, to avoid accidentally turning KCSAN on if
     the kernel is not meant to be a debug kernel;
  3. updating the short and long summaries.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

lib/Kconfig.kcsan

@@ -4,12 +4,15 @@ config HAVE_ARCH_KCSAN
 	bool
 
 menuconfig KCSAN
-	bool "KCSAN: watchpoint-based dynamic data race detector"
-	depends on HAVE_ARCH_KCSAN && !KASAN && STACKTRACE
+	bool "KCSAN: dynamic data race detector"
+	depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN
+	select STACKTRACE
 	help
-	  Kernel Concurrency Sanitizer is a dynamic data race detector, which
-	  uses a watchpoint-based sampling approach to detect races. See
-	  <file:Documentation/dev-tools/kcsan.rst> for more details.
+	  The Kernel Concurrency Sanitizer (KCSAN) is a dynamic data race
+	  detector, which relies on compile-time instrumentation, and uses a
+	  watchpoint-based sampling approach to detect data races.
+
+	  See <file:Documentation/dev-tools/kcsan.rst> for more details.
 
 if KCSAN