watchdog: add information from -watchdog help to -device help

List all watchdog devices in a separate category, and populate
their descriptions.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 1bad070..72622bd 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -26,6 +26,7 @@
     DEVICE_CATEGORY_SOUND,
     DEVICE_CATEGORY_MISC,
     DEVICE_CATEGORY_CPU,
+    DEVICE_CATEGORY_WATCHDOG,
     DEVICE_CATEGORY_MAX
 } DeviceCategory;