drm/tegra: dsi: Split out tegra_dsi_set_timeout()

In preparation for adding ganged-mode support, this commit splits out
the tegra_dsi_set_timeout() function so that it can be reused for the
slave DSI controller.

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

diff --cc drivers/gpu/drm/tegra/dsi.c
Simple merge