pstore/blk: don't depend on CONFIG_BLOCK

pstore-blk contains of two different layers:

 a) a tiny layer of sugar coating ontop of pstore-zone.  This part has
    no dependencies on the block layer, and can be used e.g. by mtd
 b) an implementation of a default fallback pstore zone backend for
    block devices

Add an ifdef for the latter so that pstore-blk itself does not have to
depend on CONFIG_BLOCK.

Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/pstore/Kconfig

@@ -164,7 +164,7 @@ config PSTORE_ZONE
 config PSTORE_BLK
 	tristate "Log panic/oops to a block device"
 	depends on PSTORE
-	depends on BLOCK
+	depends on BLOCK || !BLOCK
 	select PSTORE_ZONE
 	default n
 	help

fs/pstore/blk.c

@@ -182,6 +182,7 @@ void unregister_pstore_device(const struct pstore_zone_ops *ops)
 }
 EXPORT_SYMBOL_GPL(unregister_pstore_device);
 
+#ifdef CONFIG_BLOCK
 static struct file *psblk_file;
 
 static ssize_t psblk_generic_blk_read(char *buf, size_t bytes, loff_t pos)
@@ -269,6 +270,7 @@ void __init pstore_blk_early_init(void)
 	__pstore_blk_init(devname);
 }
 #endif /* MODULE */
+#endif /* CONFIG_BLOCK */
 
 /* get information of pstore/blk */
 int pstore_blk_get_config(struct pstore_blk_config *info)