dt-bindings: i2c: extend existing opencore bindings

Reformatted compatibility strings to one valid combination on
each line.
Add FU540-C000 specific device tree bindings to already available
i2-ocores file. This device is available on
HiFive Unleashed Rev A00 board. Move interrupt under optional
property list as this can be optional.

The FU540-C000 SoC from sifive, has an Opencore's I2C block
reimplementation.

The DT compatibility string for this IP is present in HDL and available at.
https://github.com/sifive/sifive-blocks/blob/master/src/main/scala/devices/i2c/I2C.scala#L73Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/devicetree/bindings/i2c/i2c-ocores.txt

 Device tree configuration for i2c-ocores
 
 Required properties:
-- compatible      : "opencores,i2c-ocores" or "aeroflexgaisler,i2cmst"
+- compatible      : "opencores,i2c-ocores"
+                    "aeroflexgaisler,i2cmst"
+                    "sifive,fu540-c000-i2c", "sifive,i2c0"
+                    For Opencore based I2C IP block reimplemented in
+                    FU540-C000 SoC. Please refer to sifive-blocks-ip-versioning.txt
+                    for additional details.
 - reg             : bus address start and address range size of device
-- interrupts      : interrupt number
 - clocks          : handle to the controller clock; see the note below.
                     Mutually exclusive with opencores,ip-clock-frequency
 - opencores,ip-clock-frequency: frequency of the controller clock in Hz;
@@ -12,6 +16,7 @@ Required properties:
 - #size-cells     : should be <0>
 
 Optional properties:
+- interrupts      : interrupt number.
 - clock-frequency : frequency of bus clock in Hz; see the note below.
                     Defaults to 100 KHz when the property is not specified
 - reg-shift       : device register offsets are shifted by this value