ARM: dts: AM437x: Add the internal and external clock nodes for rtc

rtc can either be supplied from internal 32k clock or external crystal
generated 32k clock. Internal clock is SOC specific and the external
clock is board dependent. Adding the corresponding nodes.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/devicetree/bindings/rtc/rtc-omap.txt

@@ -16,6 +16,8 @@ Required properties:
 Optional properties:
 - system-power-controller: whether the rtc is controlling the system power
   through pmic_power_en
+- clocks: Any internal or external clocks feeding in to rtc
+- clock-names: Corresponding names of the clocks
 
 Example:
 
@@ -26,4 +28,6 @@ rtc@1c23000 {
 		      19>;
 	interrupt-parent = <&intc>;
 	system-power-controller;
+	clocks = <&clk_32k_rtc>, <&clk_32768_ck>;
+	clock-names = "ext-clk", "int-clk";
 };