drm: xilinx: crtc/plane: Remove plane destroy function calls

The drm resources, including planes, are managed and cleaned up
by drm_mode_config_cleanup(). There's no need to destroy planes
manually.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>