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

commit 3a49012224ca9016658a831a327ff6a7fe5bb4f9 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>