drm/msm: stop storing the array of CRTCs in struct msm_drm_private

The array of CRTC in the struct msm_drm_private duplicates a list of
CRTCs in the drm_device. Drop it and use the existing list for CRTC
enumeration.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/538068/
Link: https://lore.kernel.org/r/20230519150734.3879916-1-dmitry.baryshkov@linaro.org