Avoid using inconsistent surface name of wallpaper window token

SurfaceControl doesn't support rename. And setWallpaperShowWhenLocked
is called after addWindowToken, so WallpaperWindowToken#toString
will always put mShowWhenLocked=false in the surface name. Which is
confusing if show-when-locked is set to true later.

Bug: 163976519
Flag: EXEMPT log string
Test: Set different wallpapers for home and lockscreen.
      Check dumpsys SurfaceFlinger.

Change-Id: I45f11f98d8cc052182827be06aed30470e6daf19