drm/bridge: tc358767: use DP connector if no panel set

tc358767 driver sets the connector type always to eDP.

This patch sets the type to DP if there is no panel defined, which
implies that there's a DP connector on the board.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190103115954.12785-8-tomi.valkeinen@ti.com