drm/i915: Add HDMI aspect ratio property for SDVO

Handle the HDMI aspect ratio property the same way in the SDVO code
as we handle it in the HDMI code.

v2: Remove stray whitespace change

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>