kmemleak: Do not force the slab debugging Kconfig options

Selecting DEBUG_SLAB or SLUB_DEBUG by the KMEMLEAK menu entry may cause
issues with other dependencies (KMEMCHECK). These configuration options
aren't strictly needed by kmemleak but they may increase the chances of
finding leaks. This patch also updates the KMEMLEAK config entry help
text.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>

lib/Kconfig.debug

@@ -340,8 +340,6 @@ config DEBUG_KMEMLEAK
 	bool "Kernel memory leak detector"
 	depends on DEBUG_KERNEL && EXPERIMENTAL && (X86 || ARM) && \
 		!MEMORY_HOTPLUG
-	select DEBUG_SLAB if SLAB
-	select SLUB_DEBUG if SLUB
 	select DEBUG_FS if SYSFS
 	select STACKTRACE if STACKTRACE_SUPPORT
 	select KALLSYMS
@@ -355,6 +353,9 @@ config DEBUG_KMEMLEAK
 	  allocations. See Documentation/kmemleak.txt for more
 	  details.
 
+	  Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
+	  of finding leaks due to the slab objects poisoning.
+
 	  In order to access the kmemleak file, debugfs needs to be
 	  mounted (usually at /sys/kernel/debug).