ufs: Drop dm.h header file

This header file should not be included in other header files. Remove it
and use a forward declaration instead.

Also drop asm/io.h

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/ufs/cdns-platform.c b/drivers/ufs/cdns-platform.c
index 1a7bb7b..bad1bf7 100644
--- a/drivers/ufs/cdns-platform.c
+++ b/drivers/ufs/cdns-platform.c
@@ -9,6 +9,7 @@
 #include <common.h>
 #include <dm.h>
 #include <ufs.h>
+#include <asm/io.h>
 #include <dm/device_compat.h>
 #include <linux/bitops.h>
 #include <linux/err.h>