drm/amdkfd: Use prange->list head for insert_list

There are seven list_heads in struct svm_range: list, update_list,
remove_list, insert_list, svm_bo_list, deferred_list, child_list. This
patch and the next one remove two of them that are redundant.

The insert_list head was only used for new ranges that are not on the
svms->list yet. So we can use that list head for keeping track of
new ranges before they get added, and use list_move_tail to move them
to the svms->list when ready.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>