dt-bindings: mfd: mediatek: Add MT6323 Power Controller

- Add Power Controller section to existing binding document.
- Add MT6323 PWRC bindings document with example.

Suggested-by: Frank Wunderlich <[e-mail]>
Signed-off-by: Josef Friedl <[e-mail]>
Signed-off-by: Frank Wunderlich <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/mt6397.txt

···
 - Clock
 - LED
 - Keys
+- Power controller
 
 It is interfaced to host controller using SPI interface by a proprietary hardware
 called PMIC wrapper or pwrap. MT6397/MT6323 MFD is a child device of pwrap.
···
 	Required properties:
 		- compatible: "mediatek,mt6397-keys" or "mediatek,mt6323-keys"
 	see ../input/mtk-pmic-keys.txt
+
+- power-controller
+	Required properties:
+		- compatible: "mediatek,mt6323-pwrc"
+	For details, see ../power/reset/mt6323-poweroff.txt
 
 Example:
 	pwrap: pwrap@1000f000 {

Documentation/devicetree/bindings/power/reset/mt6323-poweroff.txt

···
+Device Tree Bindings for Power Controller on MediaTek PMIC
+
+The power controller which could be found on PMIC is responsible for externally
+powering off or on the remote MediaTek SoC through the circuit BBPU.
+
+Required properties:
+- compatible: Should be one of follows
+       "mediatek,mt6323-pwrc": for MT6323 PMIC
+
+Example:
+
+       pmic {
+               compatible = "mediatek,mt6323";
+
+               ...
+
+               power-controller {
+                       compatible = "mediatek,mt6323-pwrc";
+               };
+       }