dm: i2c: Add a migration method for I2C

This probably should have been done a while back since it is a core
system. Add a migration deadline of later this year, to catch the
stragglers.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/driver-model/migration.rst b/doc/driver-model/migration.rst
index 2284e8a..8d0bb76 100644
--- a/doc/driver-model/migration.rst
+++ b/doc/driver-model/migration.rst
@@ -99,3 +99,11 @@
 The network subsystem has supported the driver model since early 2015.
 Maintainers should submit patches switching over to using CONFIG_DM_ETH and
 other base driver model options in time for inclusion in the 2020.07 release.
+
+CONFIG_DM_I2C
+-------------
+Deadline: 2021.10
+
+The I2C subsystem has supported the driver model since early 2015.
+Maintainers should submit patches switching over to using CONFIG_DM_I2C and
+other base driver model options in time for inclusion in the 2021.10 release.