drm: add backwards compatibility support for drm_kms_helper.edid_firmware

Add drm_kms_helper.edid_firmware module parameter with param ops hooks
to set drm.edid_firmware instead, for backwards compatibility.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170918182003.22238-2-jani.nikula@intel.com