When application explicitly call unmap or unmap from mmput when
application exit, driver will receive MMU_NOTIFY_UNMAP event to remove
svm range from process svms object tree and list first, unmap from GPUs
(in the following patch).

Split the svm ranges to handle partial unmapping of svm ranges. To
avoid deadlocks, updating MMU notifiers, range lists and interval trees
is done in a deferred worker. New child ranges are attached to their
parent range's child_list until the worker can update the
svm_range_list. svm_range_set_attr flushes deferred work and takes the
mmap_write_lock to guarantee that it has an up-to-date svm_range_list.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Sierra <alex.sierra@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>