RDMA/efa: Add CQ with external memory support

RDMA/efa: Add CQ with external memory support

Add an option to create CQ using external memory instead of allocating
in the driver. The memory can be passed from userspace by dmabuf fd and
an offset or a VA. One of the possible usages is creating CQs that
reside in accelerator memory, allowing low latency asynchronous direct
polling from the accelerator device. Add a capability bit to reflect on
the feature support.

Reviewed-by: Daniel Kranzdorf <dkkranzd@amazon.com>
Reviewed-by: Yonatan Nachum <ynachum@amazon.com>
Signed-off-by: Michael Margolin <mrgolin@amazon.com>
Link: https://patch.msgid.link/20250708202308.24783-4-mrgolin@amazon.com
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>