drm/tegra: dsi - Handle non-continuous clock flag

Handle the MIPI_DSI_CLOCK_NONCONTINUOUS flag and only set TX-only
clock behavior when this flag is present to allow panels requiring
continuous clock mode to operate with this driver.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>