LF-4321 drm/bridge: nwl-dsi: Avoid double modeset

When running the below system suspend/resume test case on
i.MX8ulp EVK platform with RM68200 MIPI DSI panel enabled,
panel register access would fail when the DRM connector's
DPMS property is changed from off to on after system resumes,
if the DPMS property is off before system suspends.
The root cause is that the bridge_funcs->mode_set() is called
twice during the procedure without bridge disablement, one at
system resume stage and one for DPMS on operation.  That means
the MIPI DPHY is not powered down during the procedure and
initialized/powered on twice.  As the PHY core driver takes
reference count for the power on operation, the second power
on operation doesn't take effect, hence the DPHY stays at
the initialization status.  This patch introduces a flag to
indicate if the modeset is done or not to avoid the doulbe
modeset so that the DPHY will be active when the panel registers
are accessed.

while true; do modetest -M imx-dcnano -w 34:DPMS:3; done &
while true; do /unit_tests/SRTC/rtcwakeup.out -s 2 -m mem; done

Fixes: 120ffd6b ("MLK-25574-4 drm/bridge: nwl-dsi: Get MIPI DSI controller and PHY ready in ->mode_set()")
Cc: Sandor Yu <Sandor.yu@nxp.com>
Reported-by: Zhang Bo <bo.zhang@nxp.com>
Reviewed-by: Sandor Yu <Sandor.yu@nxp.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Acked-by: Jason Liu <jason.hui.liu@nxp.com>