pinctrl: intel: Read back TX buffer state

In the same way as it's done in pinctrl-cherryview.c we would provide
a readback TX buffer state.

Fixes: 17fab473

 ("pinctrl: intel: Set pin direction properly")
Reported-by: "Bourque, Francis" <francis.bourque@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: "Bourque, Francis" <francis.bourque@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>