drm/msm: remove mdp5_cursor_plane_funcs

After converting legacy cursor updates to atomic async commits
mdp5_cursor_plane_funcs just duplicates mdp5_plane_funcs now.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Tested-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>