spi: jcore: add J-Core SPI master bindings

Signed-off-by: NRich Felker <dalias@libc.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/jcore,spi.txt

+J-Core SPI master
+
+Required properties:
+
+- compatible: Must be "jcore,spi2".
+
+- reg: Memory region for registers.
+
+- #address-cells: Must be 1.
+
+- #size-cells: Must be 0.
+
+Optional properties:
+
+- clocks: If a phandle named "ref_clk" is present, SPI clock speed
+  programming is relative to the frequency of the indicated clock.
+  Necessary only if the input clock rate is something other than a
+  fixed 50 MHz.
+
+- clock-names: Clock names, one for each phandle in clocks.
+
+See spi-bus.txt for additional properties not specific to this device.
+
+Example:
+
+spi@40 {
+	compatible = "jcore,spi2";
+	#address-cells = <1>;
+	#size-cells = <0>;
+	reg = <0x40 0x8>;
+	spi-max-frequency = <25000000>;
+	clocks = <&bus_clk>;
+	clock-names = "ref_clk";
+}