Documentation: dt: add bindings for keystone pll control controller

The main pll controller used to drive theC66x CorePacs, the switch fabric,
and a majority of the peripheral clocks (all but the ARM CorePacs, DDR3 and
the NETCP modules) requires a PLL Controller to manage the various clock
divisions, gating, and synchronization.
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
[santosh.shilimkar@ti.com: Fixed the subject line]
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

Documentation/devicetree/bindings/clock/ti-keystone-pllctrl.txt

+* Device tree bindings for Texas Instruments keystone pll controller
+
+The main pll controller used to drive theC66x CorePacs, the switch fabric,
+and a majority of the peripheral clocks (all but the ARM CorePacs, DDR3 and
+the NETCP modules) requires a PLL Controller to manage the various clock
+divisions, gating, and synchronization.
+
+Required properties:
+
+- compatible:		"ti,keystone-pllctrl", "syscon"
+
+- reg:			contains offset/length value for pll controller
+			registers space.
+
+Example:
+
+pllctrl: pll-controller@0x02310000 {
+	compatible = "ti,keystone-pllctrl", "syscon";
+	reg = <0x02310000 0x200>;
+};