sparc64: Add FORCE_MAX_ZONEORDER and default to 13

This change allows ATU (new IOMMU) in SPARC systems to request
large (32M) contiguous memory during boot for creating IOTSB backing
store.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>