usb: s/CONFIG_DM_USB/CONFIG_IS_ENABLED(DM_USB)/

This allows to disable the USB driver model in SPL because it checks
the CONFIG_SPL_DM_USB variable for SPL builds. Nothing changes for
regular non-SPL builds.

Signed-off-by: Sven Schwermer <sven@svenschwermer.de>
diff --git a/drivers/usb/musb-new/ti-musb.c b/drivers/usb/musb-new/ti-musb.c
index 9fbe2d6..ee09607 100644
--- a/drivers/usb/musb-new/ti-musb.c
+++ b/drivers/usb/musb-new/ti-musb.c
@@ -19,7 +19,7 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-#ifdef CONFIG_DM_USB
+#if CONFIG_IS_ENABLED(DM_USB)
 
 /* USB 2.0 PHY Control */
 #define CM_PHY_PWRDN			(1 << 0)
@@ -251,4 +251,4 @@
 	.bind = ti_musb_wrapper_bind,
 };
 
-#endif /* CONFIG_DM_USB */
+#endif /* CONFIG_IS_ENABLED(DM_USB) */