iommu/mediatek: Move the tlb_sync into tlb_flush

Right now, the tlb_add_flush_nosync and tlb_sync always appear together.
we merge the two functions into one(also move the tlb_lock into the new
function). No functional change.

Signed-off-by: Chao Hao <chao.hao@mediatek.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>