gennvm: Generic NVM manager

The implementation for Open-Channel SSDs is divided into media
management and targets. This patch implements a generic media manager
for open-channel SSDs. After a media manager has been initialized,
single or multiple targets can be instantiated with the media managed as
the backend.

Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/lightnvm/Makefile

@@ -3,3 +3,4 @@
 #
 
 obj-$(CONFIG_NVM)		:= core.o
+obj-$(CONFIG_NVM_GENNVM) 	+= gennvm.o