i2c: designware_i2c: Bring in the binding file

Bring in this file from Linux v5.4.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>

doc/device-tree-bindings/i2c/i2c-designware.txt

+* Synopsys DesignWare I2C
+
+Required properties :
+
+ - compatible : should be "snps,designware-i2c"
+                or "mscc,ocelot-i2c" with "snps,designware-i2c" for fallback
+ - reg : Offset and length of the register set for the device
+ - interrupts : <IRQ> where IRQ is the interrupt number.
+ - clocks : phandles for the clocks, see the description of clock-names below.
+   The phandle for the "ic_clk" clock is required. The phandle for the "pclk"
+   clock is optional. If a single clock is specified but no clock-name, it is
+   the "ic_clk" clock. If both clocks are listed, the "ic_clk" must be first.
+
+Recommended properties :
+
+ - clock-frequency : desired I2C bus clock frequency in Hz.
+
+Optional properties :
+
+ - clock-names : Contains the names of the clocks:
+    "ic_clk", for the core clock used to generate the external I2C clock.
+    "pclk", the interface clock, required for register access.
+
+ - reg : for "mscc,ocelot-i2c", a second register set to configure the SDA hold
+   time, named ICPU_CFG:TWI_DELAY in the datasheet.
+
+ - i2c-sda-hold-time-ns : should contain the SDA hold time in nanoseconds.
+   This option is only supported in hardware blocks version 1.11a or newer and
+   on Microsemi SoCs ("mscc,ocelot-i2c" compatible).
+
+ - i2c-scl-falling-time-ns : should contain the SCL falling time in nanoseconds.
+   This value which is by default 300ns is used to compute the tLOW period.
+
+ - i2c-sda-falling-time-ns : should contain the SDA falling time in nanoseconds.
+   This value which is by default 300ns is used to compute the tHIGH period.
+
+Examples :
+
+	i2c@f0000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "snps,designware-i2c";
+		reg = <0xf0000 0x1000>;
+		interrupts = <11>;
+		clock-frequency = <400000>;
+	};
+
+	i2c@1120000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "snps,designware-i2c";
+		reg = <0x1120000 0x1000>;
+		interrupt-parent = <&ictl>;
+		interrupts = <12 1>;
+		clock-frequency = <400000>;
+		i2c-sda-hold-time-ns = <300>;
+		i2c-sda-falling-time-ns = <300>;
+		i2c-scl-falling-time-ns = <300>;
+	};x
+
+	i2c@1120000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		reg = <0x2000 0x100>;
+		clock-frequency = <400000>;
+		clocks = <&i2cclk>;
+		interrupts = <0>;
+
+		eeprom@64 {
+			compatible = "linux,slave-24c02";
+			reg = <0x40000064>;
+		};
+	};