gpio: merrifield: Add support for hardware debouncer

By default all pins are configured to use a glitch filter. Writing 1 to the
certain bit of the specific register might be useful in case someone needs to
bypass the glitch filter completely for a given GPIO pin.

This patch adds support for that in the Intel Merrifield GPIO driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>