drm: xlnx: pl_disp: Added plane atomic check function

drm: xlnx: pl_disp: Added plane atomic check function

This patch adds the atomic check helper function to update mode
changed flag and returns error when framebuffer remove functionality
forces to commit without disable crtc.

Without this patch, new DRM framework commits without disable crtc
which leads image corruption and delay in consecutive runs.

Signed-off-by: Venkateshwar Rao Gannavarapu <venkateshwar.rao.gannavarapu@xilinx.com>
Reviewed-by: Hyun Kwon <hyun.kwon@xilinx.com>