iommu/exynos: Don't open-code loop unrolling

IOMMU domain allocation is not performance critical operation, so remove
hand made optimisation of unrolled initialization loop and leave this to
the compiler.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>