dt-bindings: sound: rockchip: add compatible for rk3308/px30

This patch adds bindings for rk3308/px30.
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip,pdm.txt

@@ -3,6 +3,8 @@
 Required properties:
 
 - compatible: "rockchip,pdm"
+  - "rockchip,px30-pdm"
+  - "rockchip,rk3308-pdm"
 - reg: physical base address of the controller and length of memory mapped
   region.
 - dmas: DMA specifiers for rx dma. See the DMA client binding,
@@ -12,6 +14,8 @@ Required properties:
 - clock-names: should contain following:
    - "pdm_hclk": clock for PDM BUS
    - "pdm_clk" : clock for PDM controller
+- resets: a list of phandle + reset-specifer paris, one for each entry in reset-names.
+- reset-names: reset names, should include "pdm-m".
 - pinctrl-names: Must contain a "default" entry.
 - pinctrl-N: One property must exist for each entry in
 	     pinctrl-names. See ../pinctrl/pinctrl-bindings.txt