iommu/mediatek: Move MTK_M4U_TO_LARB/PORT into mtk_iommu.c

The definition of MTK_M4U_TO_LARB and MTK_M4U_TO_PORT are shared by
all the gen2 M4U HWs. Thus, Move them out from mt8173-larb-port.h,
and put them into the c file.

Suggested-by: Honghui Zhang <honghui.zhang@mediatek.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>