drm/amd/display: fix wrong color value mapping on MCM shaper LUT

drm/amd/display: fix wrong color value mapping on MCM shaper LUT

Some shimmer/colorful points appears when using the steamOS color
pipeline for HDR on gaming with DCN32. These points look like black
values being wrongly mapped to red/blue/green values. It was caused
because the number of hw points in regular LUTs and in a shaper LUT was
treated as the same.

DCN3+ regular LUTs have 257 bases and implicit deltas (i.e. HW
calculates them), but shaper LUT is a special case: it has 256 bases and
256 deltas, as in DCN1-2 regular LUTs, and outputs 14-bit values.

Fix that by setting by decreasing in 1 the number of HW points computed
in the LUT segmentation so that shaper LUT (i.e. fixpoint == true) keeps
the same DCN10 CM logic and regular LUTs go with `hw_points + 1`.

CC: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Fixes: 4d5fd3d08ea9 ("drm/amd/display: PQ tail accuracy")
Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>