OSC can be used as USB hub source clock. An example we can route to
CLK2_P imx6 pin.

This show a usage example:

[...]
	usb_hub: usb-hub {
		compatible = "smsc,usb3503a";
		clocks = <&clks IMX6QDL_CLK_LVDS2_GATE>;
		clock-names = "refclk";
	};
};

[...]
&clks {
        assigned-clocks = <&clks IMX6QDL_CLK_LVDS2_SEL>;
        assigned-clock-parents = <&clks IMX6QDL_CLK_OSC>;
};

/sys/kernel/debug/clk/clk_summary

osc                                 5            5    24000000          0 0
[...]
    lvds2_sel                       1            1    24000000          0 0
       lvds2_gate                   1            1    24000000          0 0
[...]
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>