drm/tilcdc: Stop using struct drm_driver load() callback

Stop using struct drm_driver load() and unload() callbacks. The
callbacks should not be used anymore. Instead of using load the
drm_device is allocated with drm_dev_alloc() and registered with
drm_dev_register() only after the driver is completely initialized.
The deinitialization is done directly either in component unbind
callback or in platform driver demove callback.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>