usb: chipidea: usbmisc_imx: add imx6sx initialization routine

Except the same process with earlier imx6, it has below two features:

- Choose which vbus voltage as vbus wakeup source
We choose B_SESSION_VALID as vbus wakeup source since when the system
goes to suspend, the vbus comparator can't compare the vbus voltage
for VBUS_VALID.

- Disable dp/dm (linestate) change as wakeup source at device mode
when the vbus is not there, we don't expect dp/dm change waking up
usb controller at this situation.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>