iommu/mediatek-v1: Just rename mtk_iommu to mtk_iommu_v1

No functional change. Just rename this for readable. Differentiate this
from mtk_iommu.c

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20220503071427.2285-29-yong.wu@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>