firmware: scmi: prepare scmi uclass API to multi-channel

Changes SCMI driver API function devm_scmi_process_msg() to add
an SCMI channel reference argument for when SCMI agent supports
SCMI protocol specific channels. First argument of devm_scmi_process_msg()
is also change to point to the caller SCMI protocol device rather
than its parent device (the SCMI agent device).

The argument is a pointer to opaque struct scmi_channel known from
the SCMI transport drivers. It is currently unused and caller a pass
NULL value. A later change will enable such support once SCMI protocol
drivers have means to get the channel reference during initialization.

Cc: Lukasz Majewski <lukma@denx.de>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/include/scmi_agent-uclass.h b/include/scmi_agent-uclass.h
index a501d1b..861ac6d 100644
--- a/include/scmi_agent-uclass.h
+++ b/include/scmi_agent-uclass.h
@@ -15,7 +15,7 @@
 	/*
 	 * process_msg - Request transport to get the SCMI message processed
 	 *
-	 * @agent:		Agent using the transport
+	 * @dev:		SCMI protocol device using the transport
 	 * @msg:		SCMI message to be transmitted
 	 */
 	int (*process_msg)(struct udevice *dev, struct scmi_msg *msg);
diff --git a/include/scmi_agent.h b/include/scmi_agent.h
index 18bcd48..f4d85ca 100644
--- a/include/scmi_agent.h
+++ b/include/scmi_agent.h
@@ -13,6 +13,7 @@
 #include <asm/types.h>
 
 struct udevice;
+struct scmi_channel;
 
 /*
  * struct scmi_msg - Context of a SCMI message sent and the response received
@@ -52,10 +53,12 @@
  * On return, scmi_msg::out_msg_sz stores the response payload size.
  *
  * @dev:	SCMI device
+ * @channel:	Communication channel for the device
  * @msg:	Message structure reference
  * Return: 0 on success and a negative errno on failure
  */
-int devm_scmi_process_msg(struct udevice *dev, struct scmi_msg *msg);
+int devm_scmi_process_msg(struct udevice *dev, struct scmi_channel *channel,
+			  struct scmi_msg *msg);
 
 /**
  * scmi_to_linux_errno() - Convert an SCMI error code into a Linux errno code