drm/amd/display: Test EDID and ACPI/VBIOS readers

drm/amd/display: Test EDID and ACPI/VBIOS readers

[WHAT]
Add KUnit coverage for the EDID parsing helpers edid_extract_panel_id,
apply_edid_quirks and dm_helpers_parse_edid_caps, together with the
ACPI/VBIOS EDID readers dm_helpers_probe_acpi_edid,
dm_helpers_read_acpi_edid and dm_helpers_read_vbios_hardcoded_edid.

Assisted-by: Copilot:Claude-Opus-4.8
Reviewed-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>