dt-bindings: display: rk3288-mipi-dsi: add reset property

This reset is required in order to fully reset the internal state of the
MIPI controller.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303113945.3bd2cbd9.john@metanate.com