drm/bridge: nwl-dsi: Set PHY mode in nwl_dsi_mode_set()

The Northwest Logic MIPI DSI host controller embedded in i.MX8qxp
works with a Mixel MIPI DPHY + LVDS PHY combo to support either
a MIPI DSI display or a LVDS display.  So, this patch calls
phy_set_mode() from nwl_dsi_mode_set() to set PHY mode to MIPI DPHY
explicitly.

Cc: Guido Günther <agx@sigxcpu.org>
Cc: Robert Chiras <robert.chiras@nxp.com>
Cc: Martin Kepplinger <martin.kepplinger@puri.sm>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: NXP Linux Team <linux-imx@nxp.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Acked-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419010852.452169-2-victor.liu@nxp.com