um: Select HAVE_DEBUG_KMEMLEAK

Now we have the infrastructure to support kmemleak.
Enable the HAVE flag.
Signed-off-by: NRichard Weinberger <richard@nod.at>

arch/um/Kconfig.common

@@ -5,6 +5,7 @@ config UML
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_UID16
 	select HAVE_FUTEX_CMPXCHG if FUTEX
+	select HAVE_DEBUG_KMEMLEAK
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select GENERIC_IO