i2c: dm: Record maximum id of devices before probing devices

There is a need to find out the first free i2c ID which can be used for
i2s buses (including i2c buses connected to i2c mux). Do it early in
init and share this variable with other i2c classes for uniq bus
identification.

add from hs:
fix build problem in i2c-uclass.c for omap devices
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>
Reviewed-by: NHeiko Schocher <hs@denx.de>

drivers/i2c/i2c-uclass.c

@@ -619,6 +619,30 @@ static int i2c_child_post_bind(struct udevice *dev)
 #endif
 }
 
+struct i2c_priv {
+	int max_id;
+};
+
+int i2c_uclass_init(struct uclass *class)
+{
+	struct i2c_priv *priv = class->priv;
+
+	/* Just for sure */
+	if (!priv)
+		return -ENOMEM;
+
+	/* Get the last allocated alias. */
+#if CONFIG_IS_ENABLED(OF_CONTROL)
+	priv->max_id = dev_read_alias_highest_id("i2c");
+#else
+	priv->max_id = -1;
+#endif
+
+	debug("%s: highest alias id is %d\n", __func__, priv->max_id);
+
+	return 0;
+}
+
 UCLASS_DRIVER(i2c) = {
 	.id		= UCLASS_I2C,
 	.name		= "i2c",
@@ -626,6 +650,8 @@ UCLASS_DRIVER(i2c) = {
 #if CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)
 	.post_bind	= dm_scan_fdt_dev,
 #endif
+	.init		= i2c_uclass_init,
+	.priv_auto_alloc_size = sizeof(struct i2c_priv),
 	.post_probe	= i2c_post_probe,
 	.per_device_auto_alloc_size = sizeof(struct dm_i2c_bus),
 	.per_child_platdata_auto_alloc_size = sizeof(struct dm_i2c_chip),