tree-wide: use Device*T*ree spelling

We used both, in fact "Devicetree" was more common. But we have a general rule
that we capitalize all words in names and also we have a DeviceTree=
configuration setting, which we cannot change. If we use two different
spelllings, this will make it harder for people to use the correct one in
config files. So use the "DeviceTree" spelling everywhere.

src/udev/udev-builtin-net_id.c

@@ -924,7 +924,7 @@ static int names_devicetree(sd_device *dev, const char *prefix, EventMode mode)
                 char str[ALTIFNAMSIZ];
                 if (snprintf_ok(str, sizeof str, "%sd%u", prefix, i))
                         udev_builtin_add_property(dev, mode, "ID_NET_NAME_ONBOARD", str);
-                log_device_debug(dev, "Devicetree identifier: alias_index=%u %s \"%s\"",
+                log_device_debug(dev, "DeviceTree identifier: alias_index=%u %s \"%s\"",
                                  i, special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), str + strlen(prefix));
                 return 0;
         }