gpio: sifive: Add device tree support for GPIO generation

Add the missing bits to the yaml, dts, and Kconfig to enable GPIO pin
generation based on device tree.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>

drivers/gpio/Kconfig.sifive

@@ -8,6 +8,7 @@
 menuconfig GPIO_SIFIVE
 	bool "SiFive Freedom Processor GPIO driver"
 	depends on GPIO && SOC_RISCV32_SIFIVE_FREEDOM
+	select HAS_DTS_GPIO
 	help
 	  Enable driver for the SiFive Freedom GPIO controller.
 

dts/bindings/gpio/sifive,gpio0.yaml

@@ -30,4 +30,9 @@ properties:
       generation: define
       category: required
 
+cell_string: GPIO
+
+"#cells":
+  - pin
+  - flags
 ...

dts/riscv32/riscv32-fe310.dtsi

@@ -1,3 +1,5 @@
+#include <dt-bindings/gpio/gpio.h>
+
 / {
 	#address-cells = <1>;
 	#size-cells = <1>;
@@ -64,12 +66,14 @@
 		};
 		gpio0: gpio@10012000 {
 			compatible = "sifive,gpio0";
+			gpio-controller;
 			interrupt-parent = <&plic>;
 			interrupts = <8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
 				26 27 28 29 30 31 32 33 34 35 36 37 38 39>;
 			reg = <0x10012000 0x1000>;
 			reg-names = "control";
 			status = "disabled";
+			#gpio-cells = <2>;
 		};
 		i2c0: i2c@10016000 {
 			compatible = "sifive,i2c0";