drm/bridge: tc358767: Factor out DSI and DPI RX enablement

Factor out register programming to configure the chip video RX side for
reception of video data from DSI or DPI. This is particularly useful in
the (e)DP output mode, where the video data can be received from either
DPI or DSI. While only the former is supported in (e)DP output mode so
far, this patch is added in preparation for addition of the later.

There is a change in the order or register programming in case of the
DSI-to-DPI mode. The DSI RX side is now programmed and enabled all in
one place after the output mode has been configured. Before this change,
the DSI RX has been programmed before the output mode has been set and
only enabled afterward. The order makes no difference however, since the
DSI RX is only enabled at the end either way.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220429205644.245480-1-marex@denx.de