units: Rename systemd-udev.service to systemd-udevd.service

This naming convention is more inline with other systemd daemon
unit names (systemd-logind.service, systemd-localed.service etc)

The companion .socket units have also been renamed, however the
-trigger and -settle units keep their current name as these are
not directly related to daemon process itself.

units/.gitignore

@@ -41,5 +41,5 @@
 /emergency.service
 /systemd-udev-settle.service
 /systemd-udev-trigger.service
-/systemd-udev.service
+/systemd-udevd.service
 /debug-shell.service