Specify the wallpaper blast wrapper is a wallpaper window

SurfaceFlinger scheduler keys off the window type to implement some
refresh rate selection logic. If a layer has window type wallpaper, then
the refresh rate vote is set to min. With Blast, the actual buffer will
arrive in a layer without the window type metadata. Fix this by
setting the metadata on the blast bbq layer as well.

Test: check if wallpaper runs at a lower refresh rate
Fixes: 191222072
Change-Id: I50058cf42fca155630354ea247d12511ebfe37a8