dt-bindings: usb: add bindings doc for HiSilicon STB xHCI host controller

This commit adds bindings doc for HiSilicon STB xHCI host controller.
Signed-off-by: Jianguo Sun <sunjianguo1@huawei.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/hisilicon,histb-xhci.txt

+HiSilicon STB xHCI
+
+The device node for HiSilicon STB xHCI host controller
+
+Required properties:
+ - compatible: should be "hisilicon,hi3798cv200-xhci"
+ - reg: specifies physical base address and size of the registers
+ - interrupts : interrupt used by the controller
+ - clocks: a list of phandle + clock-specifier pairs, one for each
+	entry in clock-names
+ - clock-names: must contain
+	"bus": for bus clock
+	"utmi": for utmi clock
+	"pipe": for pipe clock
+	"suspend": for suspend clock
+ - resets: a list of phandle and reset specifier pairs as listed in
+	reset-names property.
+ - reset-names: must contain
+	"soft": for soft reset
+ - phys: a list of phandle + phy specifier pairs
+ - phy-names: must contain at least one of following:
+	"inno": for inno phy
+	"combo": for combo phy
+
+Optional properties:
+  - usb2-lpm-disable: indicate if we don't want to enable USB2 HW LPM
+  - usb3-lpm-capable: determines if platform is USB3 LPM capable
+  - imod-interval-ns: default interrupt moderation interval is 40000ns
+
+Example:
+
+xhci0: xchi@f98a0000 {
+	compatible = "hisilicon,hi3798cv200-xhci";
+	reg = <0xf98a0000 0x10000>;
+	interrupts = <GIC_SPI 69 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&crg HISTB_USB3_BUS_CLK>,
+		 <&crg HISTB_USB3_UTMI_CLK>,
+		 <&crg HISTB_USB3_PIPE_CLK>,
+		 <&crg HISTB_USB3_SUSPEND_CLK>;
+	clock-names = "bus", "utmi", "pipe", "suspend";
+	resets = <&crg 0xb0 12>;
+	reset-names = "soft";
+	phys = <&usb2_phy1_port1 0>, <&combphy0 PHY_TYPE_USB3>;
+	phy-names = "inno", "combo";
+};