pinctrl: sunxi: list all pinctrl compatible strings

List all sunxi pinctrl compatible strings in order to be able to grep for
those values.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/allwinner,sunxi-pinctrl.txt

@@ -6,8 +6,13 @@ the first two functions being GPIO in and out. The configuration on
 the pins includes drive strength and pull-up.
 
 Required properties:
-- compatible: "allwinner,<soc>-pinctrl". Supported SoCs for now are:
-  sun5i-a13.
+- compatible: Should be one of the followings (depending on you SoC):
+  "allwinner,sun4i-a10-pinctrl"
+  "allwinner,sun5i-a10s-pinctrl"
+  "allwinner,sun5i-a13-pinctrl"
+  "allwinner,sun6i-a31-pinctrl"
+  "allwinner,sun6i-a31-r-pinctrl"
+  "allwinner,sun7i-a20-pinctrl"
 - reg: Should contain the register physical address and length for the
   pin controller.