RDMA/umem: Add pinned revocable dmabuf import interface

RDMA/umem: Add pinned revocable dmabuf import interface

Added an interface for importing a pinned but revocable dmabuf.
This interface can be used by drivers that are capable of revocation
so that they can import dmabufs from exporters that may require it,
such as VFIO.

This interface implements a two step process, where drivers will first
call ib_umem_dmabuf_get_pinned_revocable_and_lock() which will pin and
map the dmabuf (and provide a functional move_notify/invalidate_mappings
callback), but will return with the lock still held so that the
driver can then populate the callback via
ib_umem_dmabuf_set_revoke_locked() without races from concurrent
revocations. This scheme also allows for easier integration with drivers
that may not have actually allocated their internal MR objects at the time
of the get_pinned_revocable* call.

Signed-off-by: Jacob Moroni <jmoroni@google.com>
Link: https://patch.msgid.link/20260305170826.3803155-4-jmoroni@google.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>