drm/i915/opregion: fix version check

The u32 version field encodes major, minor, revision and reserved. We've
basically been checking for any non-zero version.

Add opregion version logging while at it.

v2: Fix the fix of the version check

Fixes: 04ebaadb

 ("drm/i915/opregion: handle VBT sizes bigger than 6 KB")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
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/20190208184254.24123-1-jani.nikula@intel.com