reset: hisilicon: add reset-hi3660

Add hi3660 reset driver
Example of dts usage:
	iomcu_rst: iomcu_rst_controller {
		compatible = "hisilicon,hi3660-reset";
		hisi,rst-syscon = <&iomcu>;
		#reset-cells = <2>;
	};

	i2c0: i2c@..... {
                ...
		resets = <&iomcu_rst 0x20 3>; /* offset: 0x20; bit: 3 */
                ...
        };

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>