SF: Sequential display mode IDs

If the supported display modes differ after a hotplug
assing the new modes new IDs. This way the old IDs will
self invalidate.

This breaks the assumption that the modes IDs are
equivalent to indices in the array of supported modes.

Bug: 159590486
Test: manually 0. device boots in 60hz mode
               1. switch to 50hz from app
               2. disconnect display
               3. reconnect display
      dumpsys SurfaceFlinger after each step to
      verify mode IDs change as expected
Change-Id: I44c90e8151f31e998b43649dad73c51d6948195d