iommu/exynos: Refactor fault handling code

This patch provides a new implementation for page fault handing code. The
new implementation is ready for future extensions. No functional changes
have been made.

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