drm/amdkfd: Fixed kfd_process cleanup on module exit.
Handle case when module is unloaded (kfd_exit) before a process space
(mm_struct) is released.
v2: Fixed potential race conditions by removing all kfd_process from
the process table first, then working on releasing the resources.
v3: Fixed loop element access / synchronization. Fixed extra empty lines.
Signed-off-by: David Belanger <david.belanger@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>