Use only display tokens in the API to refer to new displays.
Don't require the caller to specify the display when creating
a surface (since in general a surface could be shown on
any display).
This is intended to be a minimum change just to update the API.
Note that SurfaceFlinger still uses DisplayID in a few places
internally that might cause some features not to work properly
when there are multiple displays (LayerScreenshot, for example).
Change-Id: I3d91eec2da406eefd97bcd53655d403ad865a7e6
