net: mana: Define data structures for allocating doorbell page from GDMA

The RDMA device needs to allocate doorbell pages for each user context.
Define the GDMA data structures for use by the RDMA driver.

Reviewed-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Long Li <longli@microsoft.com>
Link: https://lore.kernel.org/r/1667502990-2559-11-git-send-email-longli@linuxonhyperv.com
Acked-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>