drm/i915: Replace vbt edp.support with int_lvds_support

Replace dev_priv->vbt.edp.support with
dev_priv->vbt.int_lvds_support. We'll want to extend its
use beyond the LVDS vs. eDP case in the future.

v2: Nuke the edp.support from parse_edp() (Jani)
    Only clear int_lvds_support for gen5+ to preserve
    the current behaviour (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180508140814.20105-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>