The atomic_check is a bit too aggressive with respect to planes which
leave the active area. This caused a bunch of log spew when the cursor
got to the edge of the screen and stopped it from going all the way.

This patch removes the conservative bounds checks from atomic and clips
the dst rect such that we properly display planes which go off the
screen.

Changes in v2:
- Apply the clip to src as well (taking into account scaling)
Changes in v3:
- Use drm_atomic_helper_check_plane_state() to clip src/dst

Cc: Sravanthi Kollukuduru <skolluku@codeaurora.org>
Cc: Jeykumar Sankaran <jsanka@codeaurora.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>