Connect follower displays to lead display.

Now that the lead display is defined in the DDC, we can use this
information to connect followers to their appropriate leaders.

Bug: 265793751

Test: atest DisplayPowerControllerTest
Test: atest DisplayPowerController2Test
Change-Id: I2ef55c44ba95d3cc71c7e81d7f2c45085a369d75
8 files changed