drm/amdkfd: export svm_range_list_lock_and_flush_work

export svm_range_list_lock_and_flush_work to make other kfd parts be
able to sync svm_range_list.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>