drm/msm/mdp5: drop support for MSM8998, SDM630 and SDM660

drm/msm/mdp5: drop support for MSM8998, SDM630 and SDM660

Currently MDP5 3.x (MSM8998, SDM630 and SDM660) platforms are support
by both DPU and MDP5 drivers. Support for them in the DPU driver is
mature enough, so it's no longer sensible to keep them enabled in the
MDP5 driver. Not to mention that MSM8998 never used an MDP5 compatible
string. Drop support for the MDP5 3.x genration inside the MDP5
driver and migrate those to the DPU driver only.

Note: this will break if one uses the DT generated before v6.3 as they
had only the generic, "qcom,mdp5" compatible string for SDM630 and
SDM660. However granted that we had two LTS releases inbetween I don't
think it is an issue.

Patchwork: https://patchwork.freedesktop.org/patch/696491/
Link: https://lore.kernel.org/r/20251228-mdp5-drop-dpu3-v4-3-7497c3d39179@oss.qualcomm.com
Tested-by: Alexey Minnekhanov <alexeymin@minlexx.ru>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>