drm/msm/dpu: correct LM pairing for SM6150

The SM6150 platform doesn't have 3DMux (MERGE_3D) block, so it can not
split the screen between two LMs. Drop lm_pair fields as they don't make
sense for this platform.

Suggested-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Fixes: cb2f9144 ("drm/msm/dpu: Add SM6150 support")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/629377/
Link: https://lore.kernel.org/r/20241217-dpu-fix-sm6150-v2-1-9acc8f5addf3@linaro.org


Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>