doc: dt-binding: ci-hdrc-imx: add TPL support

TPL (Targeted Peripheral List) is needed for targets host
(OTG and Embedded Hosts) for usb certification and other
vendor specific requirements.

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