oniro-openharmony-linux.conf: Enable serial console on UART for Pi4

To enable the serial console on UART meta-raspberrypi expects to have
ENABLE_UART set. Enable it in the distro config as we do in Oniro core.

Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

conf/distro/oniro-openharmony-linux.conf

@@ -38,3 +38,7 @@ INHERIT += "uninative"
 # IMAGE_CLASSES, but doing a direct `inherit testimage` in image recipes
 # instead.
 HOSTTOOLS += "ip ping ps scp ssh stty"
+
+# Default to enabling serial debug console on RaspberryPi
+# Placed here to amend the machine config living in meta-raspberrypi
+ENABLE_UART:raspberrypi4-64 ?= "1"