drm/i915/bios: store bdb version in i915

We'll be needing the version in more places in the future, so avoid the
need to pass it around. No functional changes.

v2: Rebased

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> # v1
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c2a4189241bf0946d27e12804b1ba7d098c7d483.1615998927.git.jani.nikula@intel.com