Claude review: Revert "drm/amd/display: Remove unused cm3_helper_translate_curve_to_degamma_hw_format"

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Purpose**: Re-introduces `cm3_helper_translate_curve_to_degamma_hw_format()` which was previously removed as unused. It will be wired up in patch 3.

**Code review of the reverted function**: This is a straightforward revert of removal. The function uses 12 regions from 2^-12 to 2^0, with 16 samples per region (seg_distr[k]=4), totaling 192 hw_points. Key differences from the regamma helper:

- **Corner point slopes**: Non-zero for PQ (extrapolates to 1.0 at 10000 nits / 125 normalized), zero for everything else. The regamma helper uses zero slopes unconditionally.
- **Region range**: [2^-12, 1] for encoded input domain vs the regamma helper's much wider range for linear-light input.

**Bounds check**: `rgb_resulted` has 259 entries (`256+3`), 192 hw_points fits. The `arr_curve_points` loop at lines 449-458 iterates `k` from 0 to `MAX_REGIONS_NUMBER-1` (33), which fits the 34-entry array. The `(i >> 4) + 1 < TRANSFER_FUNC_POINTS` check at the original seg_distr=4: max index = start_index + 16 = at most 400+16 = 416 < 1025.

**Stale pointer after memset**: Lines 339-340 save `corner_points` and `rgb_resulted` as pointers into `lut_params`, then line 343 zeroes the struct. The pointers remain valid (they address fields within the struct, not separate allocations), so this is correct.

The function declaration in `dcn30_cm_common.h` is properly added. No issues.

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