drm/tegra: switch to drm_*_get(), drm_*_put() helpers
Use drm_*_get() and drm_*_put() helpers instead of drm_*_reference()
and drm_*_unreference() helpers.
drm_*_reference() and drm_*_unreference() functions are just
compatibility alias for drm_*_get() and drm_*_put() and should not be
used by new code. So convert all users of compatibility functions to
use the new APIs.