IB/mlx5: Serialize access to the VMA list

IB/mlx5: Serialize access to the VMA list

User-space applications can do mmap and munmap directly at
any time.

Since the VMA list is not protected with a mutex, concurrent
accesses to the VMA list from the mmap and munmap can cause
data corruption. Add a mutex around the list.

Cc: <[email protected]> # v4.7
Fixes: 7c2344c3bbf9 ("IB/mlx5: Implements disassociate_ucontext API")
Reviewed-by: Yishai Hadas <[email protected]>
Signed-off-by: Majd Dibbiny <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>