Add PASSENGER_DISPLAY_BRIGHTNESS property

- DISPLAY_BRIGHTNESS can send a brightness to be applied on one display.
- On multi-display devices, brightness of each display should be
  communicated separately to VHAL.
- PASSENGER_DISPLAY_BRIGHTNESS is added to serve that purpose.

Bug: 269186221
Test: build okay
Change-Id: I749ecd451afc4f24039f6e594860f1cb0fcf3509
(cherry picked from commit b9748bad)
Merged-In: I749ecd451afc4f24039f6e594860f1cb0fcf3509