Fix warnings with !CONFIG_BLOCK

Hide everything in blkdev.h with CONFIG_BLOCK isn't set, and fixup
the (few) files that fail to build because they were relying on blkdev.h
pulling in extra includes for them.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/blkdev.h

@@ -1,6 +1,8 @@
 #ifndef _LINUX_BLKDEV_H
 #define _LINUX_BLKDEV_H
 
+#ifdef CONFIG_BLOCK
+
 #include <linux/sched.h>
 #include <linux/major.h>
 #include <linux/genhd.h>
@@ -32,8 +34,6 @@
 )
 #endif
 
-#ifdef CONFIG_BLOCK
-
 struct scsi_ioctl_command;
 
 struct request_queue;