dfu: Add optional timeout parameter

When the `dfu` command is called from the U-Boot environment,
it now accepts an optional parameter that specifies a timeout (in seconds).
If a DFU connection is not made within that time the `dfu` command exits
(as it would if Ctrl+C was pressed). If the timeout is left empty or being
zero the `dfu` command behaves as it does now.

This is useful for allowing U-Boot to check to see if anything wants to
upload new firmware before continuing to boot.

The patch is based on the commit
https://github.com/01org/edison-u-boot/commit/5e966ccc3c65c18c9783741fa04e0c45e021780c
by Sebastien Colleur, which has been heavily reworked due to U-Boot changes
in the past.

Signed-off-by: Brad Campbell <bradjc5@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
diff --git a/doc/README.dfu b/doc/README.dfu
index 558d347..caf1c99 100644
--- a/doc/README.dfu
+++ b/doc/README.dfu
@@ -43,6 +43,7 @@
   CONFIG_DFU_RAM
   CONFIG_DFU_SF
   CONFIG_DFU_SF_PART
+  CONFIG_DFU_TIMEOUT
   CONFIG_DFU_VIRTUAL
   CONFIG_CMD_DFU
 
@@ -70,12 +71,15 @@
   dfu <USB_controller> [<interface> <dev>] list
     list the alternate device defined in "dfu_alt_info"
 
-  dfu <USB_controller> [<interface> <dev>]
+  dfu <USB_controller> [<interface> <dev>] [<timeout>]
     start the dfu stack on the USB instance with the selected medium
     backend and use the "dfu_alt_info" variable to configure the
     alternate setting and link each one with the medium
     The dfu command continue until receive a ^C in console or
-    a DFU detach transaction from HOST.
+    a DFU detach transaction from HOST. If CONFIG_DFU_TIMEOUT option
+    is enabled and <timeout> parameter is present in the command line,
+    the DFU operation will be aborted automatically after <timeout>
+    seconds of waiting remote to initiate DFU session.
 
   The possible values of <interface> are :
   (with <USB controller> = 0 in the dfu command example)