lightnvm: pblk: add iostat support

Since pblk registers its own block device, the iostat accounting is
not automatically done for us. Therefore, add the necessary
accounting logic to satisfy the iostat interface.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk.h

@@ -113,6 +113,7 @@ struct pblk_c_ctx {
 /* read context */
 struct pblk_g_ctx {
 	void *private;
+	unsigned long start_time;
 	u64 lba;
 };