drm/i915/dmc: protect against loading wrong firmware

In intel_package_header version 2 there's a new field in the
fw_info table that must be 0, otherwise it's not the correct DMC
firmware. Add a check for version 2 or later.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190607091230.1489-10-lucas.demarchi@intel.com