Documentation: ABI: sysfs-bus-counter: add cascade_counts_enable and external_input_phase_clock_select

This commit adds cascade_counts_enable and external_input_phase_
clock_select items to counter ABI file.
(e.g. for Renesas MTU3 hardware used for phase counting).

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230330111632.169434-4-biju.das.jz@bp.renesas.com

Documentation/ABI/testing/sysfs-bus-counter

@@ -1,3 +1,33 @@
+What:		/sys/bus/counter/devices/counterX/cascade_counts_enable
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Indicates the cascading of Counts on Counter X.
+
+		Valid attribute values are boolean.
+
+What:		/sys/bus/counter/devices/counterX/external_input_phase_clock_select
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Selects the external clock pin for phase counting mode of
+		Counter X.
+
+		MTCLKA-MTCLKB:
+			MTCLKA and MTCLKB pins are selected for the external
+			phase clock.
+
+		MTCLKC-MTCLKD:
+			MTCLKC and MTCLKD pins are selected for the external
+			phase clock.
+
+What:		/sys/bus/counter/devices/counterX/external_input_phase_clock_select_available
+KernelVersion:  6.4
+Contact:        linux-iio@vger.kernel.org
+Description:
+                Discrete set of available values for the respective device
+                configuration are listed in this file.
+
 What:		/sys/bus/counter/devices/counterX/countY/count
 KernelVersion:	5.2
 Contact:	linux-iio@vger.kernel.org
@@ -215,6 +245,8 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		This attribute indicates the number of overflows of count Y.
 
+What:		/sys/bus/counter/devices/counterX/cascade_counts_enable_component_id
+What:		/sys/bus/counter/devices/counterX/external_input_phase_clock_select_component_id
 What:		/sys/bus/counter/devices/counterX/countY/capture_component_id
 What:		/sys/bus/counter/devices/counterX/countY/ceiling_component_id
 What:		/sys/bus/counter/devices/counterX/countY/floor_component_id