iommu/exynos: Remove custom fault handler

This commit removes custom fault handler. The device drivers that
need to register fault handler can register
with iommu_set_fault_handler().

CC: Grant Grundler <grundler@chromium.org>
Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>
Signed-off-by: Shaik Ameer Basha <shaik.ameer@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>