firmware: arm_scmi: Check shmem property for channel availablity

Instead of declaring the channel availabilty unconditionally, let us
check for the presence of "shmem" property and return the channel
availablity accordingly.

Link: https://lore.kernel.org/r/20200327163654.13389-4-sudeep.holla@arm.comTested-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/smc.c

@@ -33,6 +33,11 @@ struct scmi_smc {
 
 static bool smc_chan_available(struct device *dev, int idx)
 {
+	struct device_node *np = of_parse_phandle(dev->of_node, "shmem", 0);
+	if (!np)
+		return false;
+
+	of_node_put(np);
 	return true;
 }