firmware: scmi_agent: add SCMI pin control protocol support

This patch adds SCMI pin control protocol support to make the pin
controller driver based on SCMI, such as
drivers/pinctrl/nxp/pinctrl-imx-scmi.c, can be bound to the SCMI agent
device whose protocol id is 0x19.

Signed-off-by: Alice Guo <alice.guo@nxp.com>
diff --git a/include/scmi_agent-uclass.h b/include/scmi_agent-uclass.h
index 842c568..d6586eb 100644
--- a/include/scmi_agent-uclass.h
+++ b/include/scmi_agent-uclass.h
@@ -27,6 +27,7 @@
  * @clock_dev:		SCMI clock protocol device
  * @resetdom_dev:	SCMI reset domain protocol device
  * @voltagedom_dev:	SCMI voltage domain protocol device
+ * @pinctrl_dev:	SCMI pin control protocol device
  */
 struct scmi_agent_priv {
 	u32 version;
@@ -43,6 +44,7 @@
 	struct udevice *clock_dev;
 	struct udevice *resetdom_dev;
 	struct udevice *voltagedom_dev;
+	struct udevice *pinctrl_dev;
 };
 
 static inline u32 scmi_version(struct udevice *dev)