Update ColorSpace _HLG & _PQ to use 203 nit whitepoints

Also cleans up identifying PQ & HLG transfer functions
using the same hack skia does of using negative G values
as an enum

Fixes: 272555335
Test: mapped out the curves

Change-Id: I2bd6cd0a234fdea701b85737a1378058f6c40a1b
2 files changed