drm/i915: don't init DP or HDMI when not supported by DDI port

drm/i915: don't init DP or HDMI when not supported by DDI port

There's no reason to init a DP connector if the encoder just supports
HDMI: we'll just waste hundreds and hundreds of cycles trying to do DP
AUX transactions to detect if there's something there. Same goes for a
DP connector that doesn't support HDMI, but I'm not sure these
actually exist.

v2: - Use bit fields
    - Remove useless identation level
    - Replace DRM_ERROR with DRM_DEBUG_KMS

Signed-off-by: Paulo Zanoni <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]> (v1)
Signed-off-by: Daniel Vetter <[email protected]>