drm/amdkfd: Reliably prevent reclaim-FS while holding DQM lock

This is needed to prevent deadlocks when MMU notifiers run in
reclaim-FS context and take the DQM lock for userptr evictions.
Previously this was done by making all memory allocations under
DQM locks GFP_NOIO. This is error prone. Using
memalloc_nofs_save/restore will reliably affect all memory
allocations anywhere in the kernel while the DQM lock is held.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>