RDMA/erdma: Refactor the storage structure of MTT entries

Currently our MTT only support inline mtt entries (0 level MTT) and
indirect MTT entries (1 level mtt), which will limit the maximum length
of MRs. In order to implement a multi-level MTT, we refactor the
structure of MTT first.

Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230817102151.75964-3-chengyou@linux.alibaba.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>