drm/bridge: tc358767: do a software reset if reset pin isn't connected

To get the chip into the expected state, even when the hardware reset pin
isn't connected, do a software reset in this case. It isn't as thorough as
the hardware reset, as the I2C communication block can not be reset for
obvious reasons, but it's getting the chip into a defined state.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190627085958.28331-1-l.stach@pengutronix.de