soc: imx-scu: Add SoC UID(unique identifier) support

Add i.MX SCU SoC's UID(unique identifier) support, user
can read it from sysfs:

root@imx8qxpmek:~# cat /sys/devices/soc0/soc_uid
7B64280B57AC1898

Signed-off-by: Anson Huang <[e-mail]>
Reviewed-by: Daniel Baluta <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

drivers/soc/imx/soc-imx-scu.c

···
 	} data;
 } __packed;
 
+struct imx_sc_msg_misc_get_soc_uid {
+	struct imx_sc_rpc_msg hdr;
+	u32 uid_low;
+	u32 uid_high;
+} __packed;
+
+static ssize_t soc_uid_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct imx_sc_msg_misc_get_soc_uid msg;
+	struct imx_sc_rpc_msg *hdr = &msg.hdr;
+	u64 soc_uid;
+	int ret;
+
+	hdr->ver = IMX_SC_RPC_VERSION;
+	hdr->svc = IMX_SC_RPC_SVC_MISC;
+	hdr->func = IMX_SC_MISC_FUNC_UNIQUE_ID;
+	hdr->size = 1;
+
+	ret = imx_scu_call_rpc(soc_ipc_handle, &msg, false);
+	if (ret) {
+		pr_err("%s: get soc uid failed, ret %d\n", __func__, ret);
+		return ret;
+	}
+
+	soc_uid = msg.uid_high;
+	soc_uid <<= 32;
+	soc_uid |= msg.uid_low;
+
+	return sprintf(buf, "%016llX\n", soc_uid);
+}
+
+static DEVICE_ATTR_RO(soc_uid);
+
 static int imx_scu_soc_id(void)
 {
 	struct imx_sc_msg_misc_get_soc_id msg;
···
 		ret = PTR_ERR(soc_dev);
 		goto free_revision;
 	}
+
+	ret = device_create_file(soc_device_to_device(soc_dev),
+				 &dev_attr_soc_uid);
+	if (ret)
+		goto free_revision;
 
 	return 0;