drm/tegra: sor: Make the +5V HDMI supply optional

The SOR supports multiple display modes, but only when driving an HDMI
monitor does it make sense to control the +5V power supply. eDP and DP
don't need this, so make it optional.

This fixes a crash observed during system suspend/resume.

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