drm/msm/dpu: add support for wide planes

Typically SSPP can support rectangle with width up to 2560. However it's
possible to use multirect feature and split source to use the SSPP to
output two consecutive rectangles. This commit brings in this capability
to support wider screen resolutions.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>