usb: 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 move the inline function out into a C file. We should not include C
code in headers.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/musb-new/pic32.c b/drivers/usb/musb-new/pic32.c
index 74a841a..2fbe9be 100644
--- a/drivers/usb/musb-new/pic32.c
+++ b/drivers/usb/musb-new/pic32.c
@@ -10,6 +10,7 @@
  */
 
 #include <common.h>
+#include <dm.h>
 #include <dm/device_compat.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>