clk: st: Adds quadfs clock binding

Signed-off-by: Gabriel Fernandez <[e-mail]>
Signed-off-by: Mike Turquette <[e-mail]>

Documentation/devicetree/bindings/clock/st/st,quadfs.txt

···
+Binding for a type of quad channel digital frequency synthesizer found on
+certain STMicroelectronics consumer electronics SoC devices.
+
+This version contains a programmable PLL which can generate up to 216, 432
+or 660MHz (from a 30MHz oscillator input) as the input to the digital
+synthesizers.
+
+This binding uses the common clock binding[1].
+
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+Required properties:
+- compatible : shall be:
+  "st,stih416-quadfs216",	"st,quadfs"
+  "st,stih416-quadfs432",	"st,quadfs"
+  "st,stih416-quadfs660-E",	"st,quadfs"
+  "st,stih416-quadfs660-F",	"st,quadfs"
+
+- #clock-cells : from common clock binding; shall be set to 1.
+
+- reg : A Base address and length of the register set.
+
+- clocks : from common clock binding
+
+- clock-output-names : From common clock binding. The block has 4
+                       clock outputs but not all of them in a specific instance
+                       have to be used in the SoC. If a clock name is left as
+                       an empty string then no clock will be created for the
+                       output associated with that string index. If fewer than
+                       4 strings are provided then no clocks will be created
+                       for the remaining outputs.
+
+Example:
+
+	CLOCKGEN_E: CLOCKGEN_E {
+                #clock-cells = <1>;
+                compatible = "st,stih416-quadfs660-E", "st,quadfs";
+                reg = <0xfd3208bc 0xB0>;
+
+                clocks = <&CLK_SYSIN>;
+                clock-output-names = "CLK_M_PIX_MDTP_0",
+                                        "CLK_M_PIX_MDTP_1",
+                                        "CLK_M_PIX_MDTP_2",
+                                        "CLK_M_MPELPC";
+        };