gpio: pca953x: Introduce a long awaited ->get_direction()

Introduce ->get_direction() callback for the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[Removed use of GPIOF_DIR* flags]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>