drm/tegra: sor: Implement system suspend/resume

Upon system suspend, make sure the +5V HDMI regulator is disabled. This
avoids potentially leaking current to the HDMI connector. This also
makes sure that upon resume the regulator is enabled again, which in
some cases is necessary to properly restore the state of the supply on
resume.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>