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/drivers/firmware/scmi/scmi_agent-uclass.c b/drivers/firmware/scmi/scmi_agent-uclass.c
index 3819f2f..93cfc9c 100644
--- a/drivers/firmware/scmi/scmi_agent-uclass.c
+++ b/drivers/firmware/scmi/scmi_agent-uclass.c
@@ -114,7 +114,8 @@
 	return (const struct scmi_agent_ops *)dev->driver->ops;
 }
 
-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)
 {
 	const struct scmi_agent_ops *ops;
 	struct udevice *parent = dev;