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
5e966ccc3c
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>

doc/README.dfu

@@ -43,6 +43,7 @@ Configuration Options:
   CONFIG_DFU_RAM
   CONFIG_DFU_SF
   CONFIG_DFU_SF_PART
+  CONFIG_DFU_TIMEOUT
   CONFIG_DFU_VIRTUAL
   CONFIG_CMD_DFU
 
@@ -70,12 +71,15 @@ Commands:
   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)