drm/exynos: dp: rename implementation specific driver part

The core functionality now resides in the generic bridge part so the
exynos-specific implementation details can get a more suitable nameing.

Tested-by: Caesar Wang <wxt@rock-chips.com>
Tested-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Yakir Yang <ykk@rock-chips.com>