pinctrl: baytrail: Move IRQ valid mask initialization to a dedicated callback

There is a logical continuation of the commit 5fbe5b58 ("gpio: Initialize
the irqchip valid_mask with a callback") to split IRQ initialization to
hardware and valid mask setup parts.

Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>