drivers: sensor: examplesensor: use DT_HAS_* helper

Make zephyr,examplesensor driver option dependent on it being defined in
Kconfig and set its default based on DT status as well.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

Author: gmarull

drivers/sensor/examplesensor/Kconfig

@@ -3,6 +3,7 @@
 
 config EXAMPLESENSOR
 	bool "Example sensor"
-	depends on GPIO
+	default y
+	depends on GPIO && DT_HAS_ZEPHYR_EXAMPLESENSOR_ENABLED
 	help
 	  Enable example sensor