drm/bridge: tc358767: fix single lane configuration

PHY_2LANE bit is always set in DP_PHY_CTRL, breaking 1 lane use.

Set PHY_2LANE only when 2 lanes are used.

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/20190103115954.12785-4-tomi.valkeinen@ti.com