This adds a driver core for the Realtek SMI chips and a
subdriver for the RTL8366RB. I just added this chip simply
because it is all I can test.

The code is a massaged variant of the code that has been
sitting out-of-tree in OpenWRT for years in the absence of
a proper switch subsystem. This creates a DSA driver for it.
I have tried to credit the original authors wherever
possible.

The main changes I've done from the OpenWRT code:

- Added an IRQ chip inside the RTL8366RB switch to demux and
  handle the line state IRQs.

- Distributed the phy handling out to the PHY driver.

- Added some RTL8366RB code that was missing in the driver at
  the time, such as setting up "green ethernet" with a funny
  jam table and forcing MAC5 (the CPU port) into 1 GBit.

- Select jam table and add the default jam table from the
  vendor driver, also for ASIC "version 0" if need be.

- Do not store jam tables in the device tree, store them
  in the driver.

- Pick in the "initvals" jam tables from OpenWRT's driver
  and make those get selected per compatible for the
  whole system. It's apparently about electrical settings
  for this system and whatnot, not really configuration
  from device tree.

- Implemented LED control: beware of bugs because there are
  no LEDs on the device I am using!

We do not implement custom DSA tags. This is explained in
a comment in the driver as well: this "tagging protocol" is
not simply a few extra bytes tagged on to the ethernet
frame as DSA is used to. Instead, enabling the CPU tags
will make the switch start talking Realtek RRCP internally.
For example a simple ping will make this kind of packets
appear inside the switch:

0000   ff ff ff ff ff ff bc ae c5 6b a8 3d 88 99 a2 00
0010   08 06 00 01 08 00 06 04 00 01 bc ae c5 6b a8 3d
0020   a9 fe 01 01 00 00 00 00 00 00 a9 fe 01 02 00 00
0030   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

As you can see a custom "8899" tagged packet using the
protocol 0xa2. Norm RRCP appears to always have this
protocol set to 0x01 according to OpenRRCP. You can also
see that this is not a ping packet at all, instead the
switch is starting to talk network management issues
with the CPU port.

So for now custom "tagging" is disabled.

This was tested on the D-Link DIR-685 with initramfs and
OpenWRT userspaces and works fine on all the LAN ports
(lan0 .. lan3). The WAN port is yet not working.

Cc: Antti Seppälä <a.seppala@gmail.com>
Cc: Roman Yeryomin <roman@advem.lv>
Cc: Colin Leitner <colin.leitner@googlemail.com>
Cc: Gabor Juhos <juhosg@openwrt.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>