drm/i915/bios: don't initialize fields based on vbt version

In theory, these might clobber information for older VBT versions.

We might have to store the BDB version for later parsing, but currently
all code accessing these fields will only use them on newer platforms
with new enough BDB versions.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0232d9cb258e8f83c4180cdb8aad1459a312ec2a.1506586821.git.jani.nikula@intel.com