Revert "Revert "iommu: exynos: tell kmemleak to ignore 2nd level page tables""

This reverts commit 7e20da151983c5854e15572af6d53af20f9ec4d6.
Revert "use SLAB instead of SLUB allocator?"

This reverts commit e23c3915f5a85afa9898f8c926125601f2edb5a7.