iommu/mediatek: Move reset_axi into plat_data

In mt8173 and mt8183, 0x48 is REG_MMU_STANDARD_AXI_MODE while it is
REG_MMU_CTRL in the other SoCs, and the bits meaning is completely
different with the REG_MMU_STANDARD_AXI_MODE.

This patch moves this property to plat_data, it's also a preparing
patch for mt8183.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>