vfio/pci: Add support for opregion v2.1+

Before opregion version 2.0 VBT data is stored in opregion mailbox #4,
but when VBT data exceeds 6KB size and cannot be within mailbox #4
then from opregion v2.0+, Extended VBT region, next to opregion is
used to hold the VBT data, so the total size will be opregion size plus
extended VBT region size.

Since opregion v2.0 with physical host VBT address would not be
practically available for end user and guest can not directly access
host physical address, so it is not supported.

Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Swee Yee Fonn <swee.yee.fonn@intel.com>
Signed-off-by: Fred Gao <fred.gao@intel.com>
Message-Id: <20210325170953.24549-1-fred.gao@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>