system: introduce new attribute board_name

The system board call returns the verbose model string instead of the
board name. Unfortunately we have not yet estabkushed clear convention
regarding device-tree 'compatible' or 'model' property and sysupgrade
image name (same accounts for scraping /proc/cpuinfo on legacy
targets). This is odd as the idea was to return information needed to
identify the right sysupgrade image. On most targets we got a large
shell-script which translates either /proc/cpuinfo or the 'model'
property back into the board name used here.
Hence introduce a new attribute board_name to return either
/tmp/sysinfo/board_name or /proc/device-tree/compatible.

This combines commit 79bbe6d (system: return legacy board name) and
commit 453116e (system: introduce new attribute board_name) from the
master branch into a single commit.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

system.c

@@ -115,6 +115,40 @@ static int system_board(struct ubus_context *ctx, struct ubus_object *obj,
 		fclose(f);
 	}
 
+	if ((f = fopen("/tmp/sysinfo/board_name", "r")) != NULL)
+	{
+		if (fgets(line, sizeof(line), f))
+		{
+			val = strtok(line, "\t\n");
+
+			if (val)
+				blobmsg_add_string(&b, "board_name", val);
+		}
+
+		fclose(f);
+	}
+	else if ((f = fopen("/proc/device-tree/compatible", "r")) != NULL)
+	{
+		if (fgets(line, sizeof(line), f))
+		{
+			val = strtok(line, "\t\n");
+
+			if (val)
+			{
+				next = val;
+				while ((next = strchr(next, ',')) != NULL)
+				{
+					*next = '-';
+					next++;
+				}
+
+				blobmsg_add_string(&b, "board_name", val);
+			}
+		}
+
+		fclose(f);
+	}
+
 	if ((f = fopen("/etc/openwrt_release", "r")) != NULL)
 	{
 		c = blobmsg_open_table(&b, "release");