Move BOs which are currently in a lower domain to the new
LRU before allocating backing space while validating.

This makes sure that we always have enough entries on the
LRU to allow for other processes to wait for an operation
to complete.

v2: generalize the test
v3: fix rebase error
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>