init: Support unit instancing

And use it for the logging ramfs by having a generic ramfs unit.

init.d/00_runtime.target

@@ -6,5 +6,5 @@ requires_weak = [
     "00_randd.service",
     "00_rtcd.service",
     "00_zerod.service",
-    "00_logging_ramfs.service",
+    "ramfs@logging.service",
 ]

init.d/ramfs@.service

@@ -1,8 +1,9 @@
 [unit]
+description = "$INSTANCE ramfs"
 default_dependencies = false
 requires_weak = ["00_randd.service"]
 
 [service]
 cmd = "ramfs"
-args = ["logging"]
-type = { scheme = "logging" }
+args = ["$INSTANCE"]
+type = { scheme = "$INSTANCE" }