The MediaTek MT7988 SoC comes with a built-in switch very similar to
previous MT7530 and MT7531. However, the switch address space is mapped
into the SoCs memory space rather than being connected via MDIO.
Using MMIO simplifies register access and also removes the need for a bus
lock, and for that reason also makes interrupt handling more light-weight.
Note that this is different from previous SoCs like MT7621 and MT7623N
which also came with an integrated MT7530-like switch which yet had to be
accessed via MDIO.
Split-off the part of the driver registering an MDIO driver, then add
another module acting as MMIO/platform driver.
The whole series has been tested on various MediaTek boards:
* MT7623A + MT7530 (BPi-R2)