USB: shutdown USB before booting

This patch fixes a potentially serious issue related to USB which was
discouvered by Martin Krause <martin.krause@tqs.de> and fixed for
ARM920T. Martin wrote:

  Turn off USB to prevent the host controller from writing to the
  SDRAM while Linux is booting. This could happen, because the HCCA
  (Host Controller Communication Area) lies within the SDRAM and the
  host controller writes continously to this area (as busmaster!), for
  example to increase the HccaFrameNumber variable, which happens
  every 1 ms.

This is a slightly modified version of the patch in order to shutdown
USB when booting on all architectures.

Signed-off-by: Markus Klotzbuecher <mk@denx.de>

common/cmd_bootm.c

@@ -36,6 +36,10 @@
 #include <lmb.h>
 #include <asm/byteorder.h>
 
+#if (CONFIG_COMMANDS & CFG_CMD_USB)
+#include <usb.h>
+#endif
+
 #ifdef CFG_HUSH_PARSER
 #include <hush.h>
 #endif
@@ -213,6 +217,20 @@ int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 	 */
 	iflag = disable_interrupts();
 
+#if (CONFIG_COMMANDS & CFG_CMD_USB)
+       /*
+        * turn off USB to prevent the host controller from writing to the
+        * SDRAM while Linux is booting. This could happen (at least for OHCI
+        * controller), because the HCCA (Host Controller Communication Area)
+        * lies within the SDRAM and the host controller writes continously to
+        * this area (as busmaster!). The HccaFrameNumber is for example
+        * updated every 1 ms within the HCCA structure in SDRAM! For more
+        * details see the OpenHCI specification.
+        */
+	usb_stop();
+#endif
+
+
 #ifdef CONFIG_AMIGAONEG3SE
 	/*
 	 * We've possible left the caches enabled during