Using the custom values for min. and max. luminance in transfer functions, we can reduce the
ranges of values in the shadow buffer to be limited to [0, 1], and with that we can switch
from a floating point buffer back to a normalized format. As gamma 2.2 encoding is much more
efficient at storing color values, this also drops the buffer from 16bpc down to 10bpc.
Furthermore, this offloads the gamma 2.2 -> PQ conversion to KMS when possible, and then uses
the scanout buffer with gamma 2.2 encoding directly. This way the shadow buffer gets completely
skipped and performance and efficiency get improved a lot.
BUG: 491452
CCBUG: 477223
6bd07ad6b3