samples: watchdog: add the ch32v003evt to the sample

The CH32V003 has a straight-forward watchdog that does not support
callbacks. Add an overlay and support.

To make the sample fit in flash, remove the unused logging from the
project configuration. The sample itself doesn't seem to use logging
so this is (mostly) a no-op.

Signed-off-by: Michael Hope <michaelh@juju.nz>