IB/umem: Add hugetlb flag to struct ib_umem

During ib_umem_get(), determine whether all pages from the memory
region are hugetlb pages and report this in the "hugetlb" member.
Low-level drivers can use this information if they need it.

Signed-off-by: Joachim Fenkes <fenkes@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>