drm/i915/cx0: pass encoder instead of i915 and port around

The encoder is a much more useful thing to pass around than the i915 and
port combo. Also drive-by clean up some cases where both i915 and
encoder are passed; only the latter is needed.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f9308e47a3a66bd74479480964c8a538e3f6a358.1710949619.git.jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>