gpio: revert bank bindings

Keep the words talking about what a GPIO bank is, but remove the
binding. We have not agreed that this is something we want to have.
Acked-by: NRob Herring <robh+dt@kernel.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio.txt

@@ -138,12 +138,6 @@ exposed in the device tree as an individual gpio-controller node, reflecting
 the fact that the hardware was synthesized by reusing the same IP block a
 few times over.
 
-A GPIO controller may specify a bank ID. This is a hardware index that
-indicate the logical order of the GPIO controller in the hardware architecture,
-usually in the sequence 0, 1, 2 .. n. The hardware index may be different
-from the order of register ranges and related to the backplane of how this
-one bank is connected to the outside through a pin controller for example.
-
 Optionally, a GPIO controller may have a "ngpios" property. This property
 indicates the number of in-use slots of available slots for GPIOs. The
 typical example is something like this: the hardware register is 32 bits
@@ -165,7 +159,6 @@ gpio-controller@00000000 {
 	reg = <0x00000000 0x1000>;
 	gpio-controller;
 	#gpio-cells = <2>;
-	gpio-bank = <0>;
 	ngpios = <18>;
 }