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/drivers/firmware/scmi/scmi_agent-uclass.c b/drivers/firmware/scmi/scmi_agent-uclass.c
index cc3f31d..e7ec2c1 100644
--- a/drivers/firmware/scmi/scmi_agent-uclass.c
+++ b/drivers/firmware/scmi/scmi_agent-uclass.c
@@ -97,6 +97,9 @@
 	case SCMI_PROTOCOL_ID_VOLTAGE_DOMAIN:
 		proto = priv->voltagedom_dev;
 		break;
+	case SCMI_PROTOCOL_ID_PINCTRL:
+		proto = priv->pinctrl_dev;
+		break;
 	default:
 		dev_err(dev, "Protocol not supported\n");
 		proto = NULL;
@@ -147,6 +150,9 @@
 	case SCMI_PROTOCOL_ID_VOLTAGE_DOMAIN:
 		priv->voltagedom_dev = proto;
 		break;
+	case SCMI_PROTOCOL_ID_PINCTRL:
+		priv->pinctrl_dev = proto;
+		break;
 	default:
 		dev_err(dev, "Protocol not supported\n");
 		return -EPROTO;