PCI: mvebu: Switch to using gpiod API

Switch the driver away from legacy gpio/of_gpio API to gpiod API, and
remove use of of_get_named_gpio_flags() which I want to make private to
gpiolib.

Link: https://lore.kernel.org/r/Y5EAft42YiT66mVj@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>