drm/amd/display: Shorten KUnit exported symbol names

drm/amd/display: Shorten KUnit exported symbol names

The KUnit exported helpers

  amdgpu_dm_plane_fill_gfx9_plane_attributes_from_modifiers()
  amdgpu_dm_plane_fill_gfx12_plane_attributes_from_modifiers()

exceed MODULE_NAME_LEN and cause modpost to fail with:

  ERROR: modpost: too long symbol
  "amdgpu_dm_plane_fill_gfx9_plane_attributes_from_modifiers"

Shorten the helper names while preserving their functionality.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Link: https://lore.kernel.org/all/fde3656e-9e22-4e4c-937f-7e8cb918da6b@linux.ibm.com/
Signed-off-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>