drm/i915/sdvo: Fix multi function encoder stuff

SDVO encoders can have multiple different types of outputs hanging off
them. Currently the code tries to muck around with various is_foo
flags in the encoder to figure out which type its driving. That doesn't
work with atomic and other stuff, so let's nuke those flags and just
look at which type of connector we're actually dealing with.

The is_hdmi we'll need as that's not discoverable via the output flags,
but we'll just move it under the connector.

We'll also move the sdvo fixed mode handling out from the .get_modes()
hook into the sdvo lvds init function so that we can bail out properly
if there is no fixed mode to be found.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180917151504.8754-1-ville.syrjala@linux.intel.comReviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>