Add flag to force fastboot on reset with debug board.

- Option holds the boot pin low >=10sec to force bootloader to load fastboot.
* Example: $> board/flashtools/debug_board_reset.py --fastboot

Change-Id: I48b49f01fb28725610a7d0d85afe06f5cde8bcec
diff --git a/flashtools/debug_board_reset.py b/flashtools/debug_board_reset.py
index 4d70a3d..85db6ec 100755
--- a/flashtools/debug_board_reset.py
+++ b/flashtools/debug_board_reset.py
@@ -11,6 +11,8 @@
 parser = argparse.ArgumentParser()
 parser.add_argument("--rom", help="reboot into rom",
                     action="store_true", default=False)
+parser.add_argument("--fastboot", help="reboot into fastboot",
+                    action="store_true", default=False)
 
 
 class DebugBoard(object):
@@ -51,7 +53,7 @@
     self._gpio.open_from_url(self._url, self.BOOT_NORMAL_OUTPINS)
     return self
 
-  def reset(self, boot_rom=False):
+  def reset(self, boot_rom=False, fastboot=False):
     """Reset the excelsior, and boot normal or to the ROM."""
     self._reset()
     time.sleep(0.1)
@@ -59,6 +61,10 @@
       print("Booting ROM")
       self._boot_rom()
       time.sleep(5.0)
+    elif fastboot:
+      print("Booting fastbbot")
+      self._boot_rom()
+      time.sleep(10.0)
     else:
       print("Booting LK")
       self._boot_normal()
@@ -73,7 +79,7 @@
   args = parser.parse_args()
   try:
     with DebugBoard() as board:
-      board.reset(boot_rom=args.rom)
+      board.reset(boot_rom=args.rom, fastboot=args.fastboot)
   except pyftdi.usbtools.UsbToolsError:
     print("*" * 70)
     print("Unable to connect to debug board, check connection or manually toggle GPIO.")