drm/tilcdc: panel: fix leak when unloading the module

commit 3a490122 upstream.

The driver did not unregister the allocated framebuffer, which caused
memory leaks (and memory manager WARNs) when unloading. Also, the
framebuffer device under /dev still existed after unloading.

Add a call to drm_fbdev_cma_fini when unloading the module to prevent
both issues.

Signed-off-by: Guido Martínez <guido@vanguardiasur.com.ar>
Tested-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>