drm/msm/dpu: don't try using 2 LMs if only one DSC is available

drm/msm/dpu: don't try using 2 LMs if only one DSC is available

Current topology code will try using 2 LMs with just one DSC, which
breaks cases like SC7280 / Fairphone5. Forbid using 2 LMs split in such
a case.

Fixes: 1ce69c265a53 ("drm/msm/dpu: move resource allocation to CRTC")
Reported-by: Luca Weiss <luca.weiss@fairphone.com>
Closes: https://lore.kernel.org/r/DH1IKLU0YZYU.2SW4WYO7H3H4R@fairphone.com/
Tested-by: Luca Weiss <luca.weiss@fairphone.com> # qcm6490-fairphone-fp5
Patchwork: https://patchwork.freedesktop.org/patch/712386/
Link: https://lore.kernel.org/r/20260317-fix-3d-dsc-v1-1-88b54f62f659@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>