drm/tilcdc: disable crtc on unload

Disable crtc on unload. Call tilcdc_crtc_dpms() with DRM_MODE_DPMS_OFF
in the beginning of unload function.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
[Added description to the patch]
Signed-off-by: Jyri Sarha <jsarha@ti.com>