usb: fusb302: Convert to use GPIO descriptors

This converts the FUSB302 driver to use GPIO descriptors.
The conversion to descriptors per se is pretty straight-forward.

In the process I discovered that:

1. The driver uses a completely undocumented device tree binding
   for the interrupt GPIO line, "fcs,int_n". Ooops.

2. The undocumented binding, presumably since it has not seen
   review, is just "fcs,int_n", lacking the compulsory "-gpios"
   suffix and also something that is not a good name because
   the "_n" implies the line is inverted which is something we
   handle with flags in the device tree. Ooops.

3. Possibly the driver should not be requesting the line as a
   GPIO and request the corresponding interrupt line by open
   coding, the GPIO chip is very likely doubleing as an IRQ
   controller and can probably provide an interrupt directly
   for this line with interrupts-extended = <&gpio0 ...>;

4. Possibly the IRQ should just be tagged on the I2C client node
   in the device tree like apparently ACPI does, as it overrides
   this IRQ with client->irq if that exists.

But now it is too late to do much about that and as I can see
this is used like this in the Pinebook which is a shipping product
so let'a just contain the mess and move on.

The property currently appears in:
arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts

Create a quirk in the GPIO OF library to allow this property
specifically to be specified without the "-gpios" suffix, we have
other such bindings already.

Cc: Tobias Schramm <t.schramm@manjaro.org>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Yueyao Zhu <yueyao@google.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20200415192448.305257-1-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>