usb: Do not compile USB_STORAGE with BLK && !DM_USB

The USB storage driver does not compile when CONFIG_BLK is set,
but DM_USB is not set, as we're missing the DM device links for
CONFIG_BLK enabled code paths.

So far it looks like nobody fell into this trap, because no board
enabled CONFIG_BLK and CONFIG_USB_STORAGE while not enabling
CONFIG_DM_USB, but we should still reflect that dependency properly
in Kconfig so that implicit enabling of CONFIG_USB_STORAGE works.

Signed-off-by: Alexander Graf <agraf@suse.de>

drivers/usb/Kconfig

@@ -70,6 +70,7 @@ comment "USB peripherals"
 
 config USB_STORAGE
 	bool "USB Mass Storage support"
+	depends on !(BLK && !DM_USB)
 	---help---
 	  Say Y here if you want to connect USB mass storage devices to your
 	  board's USB port.