keventd: read udev database records by devpath

udevdb_read_parent() contained the general capability, keyed from
sysfs when no uevent is in hand.  Split it out as
udevdb_read_devpath() for the D-Bus Info method; parent lookup
becomes a wrapper.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

keventd/udevdb.h

@@ -57,6 +57,11 @@ int  udevdb_read   (struct uevent *ev);
  */
 int  udevdb_read_parent (struct uevent *ev);
 
+/*
+ * Like udevdb_read(), for any devpath, keyed from sysfs.
+ */
+int  udevdb_read_devpath(const char *devpath, struct uevent *ev);
+
 /*
  * Delete a device's database entry on ACT_REMOVE.
  */