OMAPDSS: DSI: Add function to set panel size for command mode panels

DSI command mode panels don't need to configure a full set of timings to
configure DSI, they only require the width and the height of the panel in
pixels.

Use omapdss_dsi_set_size for command mode panels, omapdss_dsi_set_timings is
meant for video mode panels. When performing rotation via chaning the address
mode of the panel, we would need to swap width and height when doing 90 or 270
rotation. Make sure that omapdss_dsi_set_size() makes the new width and height
visible to DSI.

Signed-off-by: Archit Taneja <archit@ti.com>