dt-bindings: input: mtk-pmic-keys: add MT6358 binding definition

Add the binding documentation of the mtk-pmic-keys for the MT6358 PMICs.

MT6358 is a little different since it used separate IRQs for the
release key (_r) event

Signed-off-by: Mattijs Korpershoek <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/devicetree/bindings/input/mtk-pmic-keys.txt

···
 Documentation/devicetree/bindings/mfd/mt6397.txt
 
 Required properties:
-- compatible: "mediatek,mt6397-keys" or "mediatek,mt6323-keys"
+- compatible: Should be one of:
+	- "mediatek,mt6397-keys"
+	- "mediatek,mt6323-keys"
+	- "mediatek,mt6358-keys"
 - linux,keycodes: See Documentation/devicetree/bindings/input/input.yaml
 
 Optional Properties: