usb: ehci: add freescale imx28 special write register method

According to Freescale imx28 Errata, "ENGR119653 USB: ARM to USB
register error issue", All USB register write operations must
use the ARM SWP instruction. So, we implement a special ehci_write
for imx28.

Discussion for it at below:
http://marc.info/?l=linux-usb&m=137996395529294&w=2



Without this patcheset, imx28 works unstable at high AHB bus loading.
If the bus loading is not high, the imx28 usb can work well at the most
of time. There is a IC errata for this problem, usually, we consider
IC errata is a problem not a new feature, and this workaround is needed
for that, so we need to add them to stable tree 3.11+.

Cc: stable@vger.kernel.org
Cc: robert.hodaszi@digi.com
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>