drm/rockchip: dw-mipi-dsi: pass mode in where needed

This shows that we only use the mode from the enable function and
prepares us to remove the "mode" field and the mode_set hook in the next
commit.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Chris Zhong <zyw@rock-chips.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170224125506.21533-3-john@metanate.com