network: set timeline for CONFIG_DM_ETH conversion

The driver model has been supported for network drivers since 2015. It is
time to convert the remaining boards. Set July 2020 as a timeline.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/Makefile b/Makefile
index c02accf..ae56e47 100644
--- a/Makefile
+++ b/Makefile
@@ -1026,6 +1026,17 @@
 	@echo >&2 "===================================================="
 endif
 endif
+ifneq ($(CONFIG_NET),)
+ifneq ($(CONFIG_DM_ETH),y)
+	@echo >&2 "===================== WARNING ======================"
+	@echo >&2 "This board does not use CONFIG_DM_ETH (Driver Model"
+	@echo >&2 "for Ethernet drivers). Please update the board to use"
+	@echo >&2 "CONFIG_DM_ETH before the v2020.07 release. Failure to"
+	@echo >&2 "update by the deadline may result in board removal."
+	@echo >&2 "See doc/driver-model/migration.rst for more info."
+	@echo >&2 "===================================================="
+endif
+endif
 	@# Check that this build does not use CONFIG options that we do not
 	@# know about unless they are in Kconfig. All the existing CONFIG
 	@# options are whitelisted, so new ones should not be added.