dfu: Introduce CONFIG_BOOT_WAIT_FOR_USB_DFU

This Kconfig parameter makes MCUboot wait for a prescribed duration
of time to allow for USB DFU to be invoked.

Signed-off-by: Rajavardhan Gundi <rajavardhan.gundi@intel.com>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 77c5b63..29193d1 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -122,6 +122,17 @@
 	 on some hardware that has long erase times, to prevent long wait
 	 times at the beginning of the DFU process.
 
+config BOOT_WAIT_FOR_USB_DFU
+	bool "Wait for a prescribed duration to see if USB DFU is invoked"
+	default n
+	select USB
+	select USB_DFU_CLASS
+	select IMG_MANAGER
+	help
+	  If y, MCUboot waits for a prescribed duration of time to allow
+	  for USB DFU to be invoked. Please note DFU always updates the
+	  slot1 image.
+
 config ZEPHYR_TRY_MASS_ERASE
 	bool "Try to mass erase flash when flashing MCUboot image"
 	default y