usb: Tidy up the usb_start flag

This should be declared in a header file so that type-checking works
correctly.

Add a single declaration to usb.h and remove the others.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/test/boot/bootdev.c b/test/boot/bootdev.c
index 8cf3f30..606bf4f 100644
--- a/test/boot/bootdev.c
+++ b/test/boot/bootdev.c
@@ -19,9 +19,9 @@
 
 /* Allow reseting the USB-started flag */
 #if defined(CONFIG_USB_HOST) || defined(CONFIG_USB_GADGET)
-extern char usb_started;
+extern bool usb_started;
 #else
-char usb_started;
+#include <usb.h>
 #endif
 
 /* Check 'bootdev list' command */
diff --git a/test/dm/blk.c b/test/dm/blk.c
index 0aa04c6..446c442 100644
--- a/test/dm/blk.c
+++ b/test/dm/blk.c
@@ -16,9 +16,6 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-/* Allow resetting the USB-started flag */
-extern char usb_started;
-
 /* Test that block devices can be created */
 static int dm_test_blk_base(struct unit_test_state *uts)
 {