dt-bindings: pinctrl: aspeed: Add g4 USB functions

dt-bindings: pinctrl: aspeed: Add g4 USB functions

The AST2400 contains several USB controllers:

* USB 1.1 Host Controller
* USB 2.0 Host Controller
* USB 2.0 Virtual Hub
* USB 1.1 HID Controller

Pins for three ports are routed to the three controllers such that:

* Port 1 is a dedicated USB 1.1 host port
* Port 2 is shared between the USB 1.1 host and HID controllers
* Port 3 is shared between the USB 2.0 host and Hub controllers

As the pins for port 1 are fixed function there is no associated mux
function or group described in the bindings. Ports 2 and 3 are muxed as
above, and the table below describes the mapping between pinmux function
names and ports:

Port  | USB Version  | USB Mode  | Mux Function
------|--------------|-----------|-------------
1     | 1.1          | Host      | -
2     | 1.1          | Host      | USB11H2
2     | 1.1          | HID       | USB11D1
3     | 2.0          | Host      | USB2H1
3     | 2.0          | Device    | USB2D1

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>