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Originally we remapped temperatures to a range [5700, 7500) and then
computed RGB scale factors using linear functions.

The table that remaps temperatures has been updated with
crrev.com/c/2001254 but we didn't update the code to accept the new range
[4500, 7500).

This CL updates the accepted range and also recomputes GB coefficients
used for the linear regression in the interval [4500, 6500].

Bug: 1045647
Test: ash_unittests --gtest_filter=AmbientTemperature.AmbientTemperatureToRGBScaleFactors
Change-Id: Ifa19820cd8d6b076dbf6c85841f126bca7ea4585
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2022246Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736498}