VMDK: enable twoGbMaxExtentFlat Enable the createType 'twoGbMaxExtentFlat'. The supporting code is already in. Signed-off-by: Fam Zheng <famcool@gmail.com> Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>