drm/msm/mdp5: negative x/y in cursor move

modesetting X11 driver may provide negative x/y cordinates in
mdp5_crtc_cursor_move call when rotation is enabled.

Cursor buffer can overlap down to its negative width/height.

ROI has to be recalculated for negative x/y indicating using the
lower/right corner of the cursor buffer and hotspot must be set
in MDP5_LM_CURSOR_XY_SRC_Y MDP5_LM_CURSOR_XY_SRC_X.

Signed-off-by: Carsten Behling <carsten.behling@gmail.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>