This patch adds decriptions for mt2712 IOMMU and SMI.

In order to balance the bandwidth, mt2712 has two M4Us, two
smi-commons, 10 smi-larbs. and mt2712 is also MTK IOMMU gen2 which
uses ARM Short-Descriptor translation table format.

The mt2712 M4U-SMI HW diagram is as below:

                            EMI
                             |
              ------------------------------------
              |                                  |
             M4U0                              M4U1
              |                                  |
         smi-common0                        smi-common1
              |                                  |
  -------------------------       --------------------------------
  |     |     |     |     |       |         |        |     |     |
  |     |     |     |     |       |         |        |     |     |
larb0 larb1 larb2 larb3 larb6    larb4    larb5    larb7 larb8 larb9
disp0 vdec  cam   venc   jpg  mdp1/disp1 mdp2/disp2 mdp3 vdo/nr tvd

All the connections are HW fixed, SW can NOT adjust it.
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>