lightnvm: do not compile in debugging by default

The LightNVM module exposes a debug interface when CONFIG_NVM_DEBUG is
set. This interfaces takes a string to configure media managers and
targets. Make sure this interface is only exposed when chosen
deliberately.
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/lightnvm/Kconfig

@@ -18,6 +18,7 @@ if NVM
 
 config NVM_DEBUG
 	bool "Open-Channel SSD debugging support"
+	default n
 	---help---
 	Exposes a debug management interface to create/remove targets at: