ramips: adding registration for si3210

The si3210 is a SLIC device providing a complete analog telephone
interface and therefore frequently used in soho router.
The si3210 have a native spi interface to be controlled by the CPU
but currently there is no dedicated driver in lede.
Adding a registration for this device in spidev allow to control the
device in user space.
This way of patching is also in line with the rationale of the spidev
driver, see: http://marc.info/?t=148145791900001&r=1&w=2
The si3210 has been also added in the DWR-512 DT to properly describe
the HW.

Signed-off-by: Giuseppe Lippolis <giu.lippolis@gmail.com>

target/linux/generic/patches-4.4/105-add-linux-spidev-compatible.patch

@@ -0,0 +1,15 @@
+Add the linux,spidev compatible in spidev
+Several device in ramips have this binding in the dts
+
+Signed-off-by: Giuseppe Lippolis <giu.lippolis@gmail.com>
+---
+--- a/drivers/spi/spidev.c	2016-12-11 09:43:30.502270523 +0100
++++ b/drivers/spi/spidev.c	2016-12-11 09:45:54.688430012 +0100
+@@ -695,6 +695,7 @@ static struct class *spidev_class;
+ static const struct of_device_id spidev_dt_ids[] = {
+ 	{ .compatible = "rohm,dh2228fv" },
+ 	{ .compatible = "lineartechnology,ltc2488" },
++	{ .compatible = "siliconlabs,si3210" },
+ 	{},
+ };
+ MODULE_DEVICE_TABLE(of, spidev_dt_ids);

target/linux/ramips/dts/DWR-512-B.dts

@@ -104,6 +104,19 @@
 	};
 };
 
+&spi1 {
+	status = "okay";
+
+	spidev@1 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "siliconlabs,si3210";
+
+		reg = <0>;
+		spi-max-frequency = <1000000>;
+	};
+};
+
 &pinctrl {
 	state_default: pinctrl0 {
 		gpio {