Plumb display brightness nits to composer hal.

OEM feedback was that the display brightness in nits should be known to
the Hardware Composer for correct tone-mapping behavior by the DPU.
Inteperpolating the display brightness curve that's defined in display
config files is possible, but it would require the vendor to re-implement
DisplayManager logic for interpolating a spline curve.

Bug: 220396224
Test: builds, boots
Change-Id: I28d936c118bed1184d4f742478c8862f9e0aba95