rockchip: include: grf: Add GRF register declaration for mipi dsi

Add GRF register declaration for mipi dsi.

Signed-off-by: Eric Gao <eric.gao@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>