dt-bindings: Add devicetree bindings

Add snapshot of device tree bindings from keystone common kernel, branch
"android-mainline-keystone-qcom-release" at c4c12103f9c0 ("Snap for 9228065
from e32903b9a63bb558df8b803b076619c53c16baad to
android-mainline-keystone-qcom-release").

Change-Id: I7682079615cbd9f29340a5c1f2a1d84ec441a1f1
Signed-off-by: Melody Olvera <quic_molvera@quicinc.com>

bindings/pps/pps-gpio.txt

@@ -0,0 +1,30 @@
+Device-Tree Bindings for a PPS Signal on GPIO
+
+These properties describe a PPS (pulse-per-second) signal connected to
+a GPIO pin.
+
+Required properties:
+- compatible: should be "pps-gpio"
+- gpios: one PPS GPIO in the format described by ../gpio/gpio.txt
+
+Additional required properties for the PPS ECHO functionality:
+- echo-gpios: one PPS ECHO GPIO in the format described by ../gpio/gpio.txt
+- echo-active-ms: duration in ms of the active portion of the echo pulse
+
+Optional properties:
+- assert-falling-edge: when present, assert is indicated by a falling edge
+                       (instead of by a rising edge)
+
+Example:
+	pps {
+		pinctrl-names = "default";
+		pinctrl-0 = <&pinctrl_pps>;
+
+		gpios = <&gpio1 26 GPIO_ACTIVE_HIGH>;
+		assert-falling-edge;
+
+		echo-gpios = <&gpio1 27 GPIO_ACTIVE_HIGH>;
+		echo-active-ms = <100>;
+
+		compatible = "pps-gpio";
+	};