Input: sun4i-ts - add support for temperature sensor

The sun4i resisitive touchscreen controller also comes with a built-in
temperature sensor. This commit adds support for it.

This commit also introduces a new "ts-attached" device-tree property,
when this is not set, the input part of the driver won't register. This way
the internal temperature sensor can be used to measure the SoC temperature
independent of there actually being a touchscreen attached to the controller.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
index 41f8b59..746d3c56 100644
--- a/drivers/input/touchscreen/Kconfig
+++ b/drivers/input/touchscreen/Kconfig
@@ -900,6 +900,7 @@
 config TOUCHSCREEN_SUN4I
 	tristate "Allwinner sun4i resistive touchscreen controller support"
 	depends on ARCH_SUNXI || COMPILE_TEST
+	depends on HWMON
 	help
 	  This selects support for the resistive touchscreen controller
 	  found on Allwinner sunxi SoCs.