drm/msm/disp: set num_planes to 1 for interleaved YUV formats

drm/msm/disp: set num_planes to 1 for interleaved YUV formats

Interleaved YUV formats use only one plane for all pixel data. Specify
num_planes = 1 for those formats. This was left unnoticed since
_dpu_format_populate_plane_sizes_linear() overrides layout->num_planes.

Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
Reviewed-by: Jessica Zhang <jessica.zhang@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/688162/
Link: https://lore.kernel.org/r/20251114-dpu-formats-v3-1-cae312379d49@oss.qualcomm.com
Tested-by: Luca Weiss <luca.weiss@fairphone.com> # qcm6490-fairphone-fp5
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>