drm/komeda: Add drm_lut_to_fgamma_coeffs()

This function is used to convert drm color lut to komeda HW required curve
coeffs values.

Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Reviewed-by: Mihail Atanassov <mihail.atanassov@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112110927.20931-3-james.qian.wang@arm.com