drm/msm/dp: Prepare for link training per-segment for LTTPRs

drm/msm/dp: Prepare for link training per-segment for LTTPRs

Per-segment link training requires knowing the number of LTTPRs
(if any) present. Store the count during LTTPRs' initialization.

Fixes: 72d0af4accd9 ("drm/msm/dp: Add support for LTTPR handling")
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@gmail.com>
Tested-by: Jessica Zhang <quic_jesszhan@quicinc.com> # SA8775P
Tested-by: Johan Hovold <johan+linaro@kernel.org>
Tested-by: Rob Clark <robdclark@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/652306/
Link: https://lore.kernel.org/r/20250507230113.14270-4-alex.vinarskis@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>