kmemcheck: make kconfig accessible for other architectures

The Kconfig options of kmemcheck are hidden under arch/x86 which makes porting
to other architectures harder. To fix that, move the Kconfig bits to
lib/Kconfig.kmemcheck and introduce a CONFIG_HAVE_ARCH_KMEMCHECK config option
that architectures can define.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 399ba81..6b0c2d8a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -996,3 +996,5 @@
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
+
+source "lib/Kconfig.kmemcheck"