treewide: Test on CONFIG_USB_HOST (or CONFIG_CMD_USB) not CONFIG_USB

As the logic here is only used when we have a USB host controller, test
on CONFIG_USB_HOST rather than CONFIG_USB in general.  This lets us move
towards using CONFIG_USB only as a menu symbol to say that we have some
form of USB, and then USB_HOST or USB_GADGET depending on the role that
USB plays within the build.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/stm32mp1.h b/include/configs/stm32mp1.h
index 2e7f49e..b372838 100644
--- a/include/configs/stm32mp1.h
+++ b/include/configs/stm32mp1.h
@@ -101,7 +101,7 @@
 #define BOOT_TARGET_UBIFS(func)
 #endif
 
-#ifdef CONFIG_USB
+#ifdef CONFIG_CMD_USB
 #define BOOT_TARGET_USB(func)	func(USB, usb, 0)
 #else
 #define BOOT_TARGET_USB(func)