drm/tegra: Use tegra_commit_dc() in output drivers

All output drivers have open-coded variants of this function, so export
it to remove some code duplication.

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

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

diff --cc drivers/gpu/drm/tegra/drm.h
Simple merge

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

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

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

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