drm/panel: simple: Add support for Samsung LTN140AT29 panel

This panel is used by the Nyan Blaze board and can be supported by the
simple-panel driver.

Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
[tomeu.vizoso@collabora.com: add device tree binding document]
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>