HWC2: Modify multidisplay for null display mode

Rename CreateBuiltInDisplays to HandleBuiltInDisplays
Return 0 supported virtual displays
Bailout of BuiltIn and Pluggable handlers

Change-Id: I16ee9ce07cf162a3b54dba0cacc38c4c37f87872
CRs-Fixed: 2333745
2 files changed