drm/vc4: hdmi: Move vc4_hdmi_supports_scrambling() around

We'll need it earlier in the driver, so let's move it next to the other
scrambling-related helpers.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220829134731.213478-7-maxime@cerno.tech