drm/i915/bios: add intel_bios_encoder_data to encoder, use for iboost

Add intel_bios_encoder_data pointer to encoder, and use it for hdmi and
dp iboost. For starters, we only set the encoder->devdata for DDI
encoders, i.e. we can only use it for data that is used by DDI encoders.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4bc49244ce68e136e5b21db4c4e6554bec9ac0fb.1615998927.git.jani.nikula@intel.com