RDMA/uverbs: Convert the write interface to use uverbs_api

This organizes the write commands into objects and links them to the
uverbs_api data structure. The command path is reworked to use uapi
instead of its internal structures.

The command mask is moved from a runtime check to a registration time
check in the uapi.

Since the write interface does not have the object ID as part of the
command, the radix bins are converted into linear lists to support the
lookup.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>