libhwc2.1: restrict the external display to a single DPP configuration

There is flickring issue when the external display has mixed composition
type. To avoid it, HWC restricts the external display to a single DDP
configuration to have the same composition type.

Bug: 311578920
Test: check the mini player case
Change-Id: If0b0d834b0a3568df50dbebf1762fdb2103f773c
2 files changed