drm/mediatek: Switch the hdmi bridge ops to the atomic versions

The bridge operation '.enable' and the audio cb '.get_eld'
access hdmi->conn. In the future we will want to support
the flag DRM_BRIDGE_ATTACH_NO_CONNECTOR and then we will
not have direct access to the connector.
The atomic version '.atomic_enable' allows accessing the
current connector from the state.
This patch switches the bridge to the atomic version to
prepare access to the connector in later patches.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>