drm/exynos: enable out_bridge in exynos_dsi_enable

As the out bridge will not be enabled directly by the framework,
it should be enabled by DSI. exynos_dsi_enable() should handle a case,
when there is an out_bridge connected as a DSI peripheral.

Changed in v5:
- fixed error path in exynos_dsi_enable

Signed-off-by: Maciej Purski <m.purski@samsung.com>
[ a.hajda@samsung.com: v5 ]
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>