mlx5: Extend mlx5dv_get_qp() to return UAR mapping info

[khng]

Summary

Extend mlx5dv_get_qp() to return UAR mapping info. This can allow a
process to share its doorbell access with secondary process by re-mmap
the UAR address on the device and make it accessible as a user space
address.

Signed-off-by: Xueming Li <[e-mail]>
Reviewed-by: Yishai Hadas <[e-mail]>

[khng: Cherry-picked from rdma-core
14d0beecc574d80e17131bded11e18f39d45ae46]

[khng]

Update description.

[kib]

Does this change requires bump of libmlx5.so version? I hope not, but it looks like it might.