tegra: i2c: Add function to find DVC bus

Add tegra_i2c_get_dvc_bus_num() to obtain the I2C bus number of DVC bus.
This allows us to talk to the PMU.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/drivers/i2c/tegra_i2c.c b/drivers/i2c/tegra_i2c.c
index 21f6897..5b6ea0e 100644
--- a/drivers/i2c/tegra_i2c.c
+++ b/drivers/i2c/tegra_i2c.c
@@ -567,3 +567,17 @@
 	return 0;
 }
 #endif
+
+int tegra_i2c_get_dvc_bus_num(void)
+{
+	int i;
+
+	for (i = 0; i < CONFIG_SYS_MAX_I2C_BUS; i++) {
+		struct i2c_bus *bus = &i2c_controllers[i];
+
+		if (bus->inited && bus->is_dvc)
+			return i;
+	}
+
+	return -1;
+}