md: move the early init autodetect code to drivers/md/

Just like the NFS and CIFS root code this better lives with the
driver it is tightly integrated with.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/raid/detect.h

@@ -1,3 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
 void md_autodetect_dev(dev_t dev);
+
+#ifdef CONFIG_BLK_DEV_MD
+void md_run_setup(void);
+#else
+static inline void md_run_setup(void)
+{
+}
+#endif