drm/amd/display: Extract shared KUnit test helpers

Extract common allocation and setup patterns from KUnit test
files into a dedicated helpers module to reduce duplication.

Add tests/amdgpu_dm_kunit_helpers.c with shared helpers:
- dm_kunit_alloc_adev: allocate amdgpu_device via DRM mock
- dm_kunit_alloc_link: allocate zeroed dc_link
- dm_kunit_alloc_link_with_ctx: allocate dc_link with dc_context
- dm_kunit_alloc_dm: allocate display_manager with DC state
- dm_kunit_alloc_stream: allocate dc_stream_state with link
- dm_kunit_add_stream_to_state: wire stream into dc_state
- dm_kunit_alloc_connector: allocate connector wired to device

Update 10 test files to use the shared helpers, removing
duplicated local alloc_test_adev, alloc_test_link,
alloc_test_dm, alloc_test_stream, and add_test_stream
functions.

Add missing MODULE_DESCRIPTION() macro to suppress modpost warning:
WARNING: modpost: missing MODULE_DESCRIPTION() in
amdgpu_dm_kunit_helpers.o

Assisted-by: Copilot:Claude-Opus-4.6
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>

0 files changed, 0 insertions, 0 deletions