Accomodate brightness space change for client target

Previous the hal reported a white point in nits. Since nits are being
removed from the composer interface, SurfaceFlinger converts a dimming
ratio reported by composer into a white point instead.

Bug: 217961164
Test: builds, boots
Change-Id: I9ceec3af80f503df0debe434bb454ec42694811b
Merged-In: I9ceec3af80f503df0debe434bb454ec42694811b