usb: chipidea: imx: enable CI_HDRC_SET_NON_ZERO_TTHA

For i.mx platform, set ttctrl.ttha with non-zero value only affects
sitd, and ehci core makes sure the schedule is not full when accepts
new request, so it will not occur the transaction which will acorss
the SoF.

Signed-off-by: Peter Chen <peter.chen@freescale.com>