net: dsa: mt7530: support the 7530 switch on the Mediatek MT7621 SoC

net: dsa: mt7530: support the 7530 switch on the Mediatek MT7621 SoC

The MediaTek MT7621 SoC device contains a 7530 switch, and the existing
linux kernel 7530 DSA switch driver can be used with it.

The bulk of the changes required stem from the 7621 having different
regulator and pad setup. The existing setup of these in the 7530
driver appears to be very specific to its implemtation in the Mediatek
7623 SoC. (Not entirely surprising given the 7623 is a quad core ARM
based SoC, and the 7621 is a dual core, dual thread MIPS based SoC).

Create a new devicetree type, "mediatek,mt7621", to support the 7530
switch in the 7621 SoC. There appears to be no usable ID register to
distinguish it from a 7530 in other hardware at runtime. This is used
to carry out the appropriate configuration and setup.

Signed-off-by: Greg Ungerer <gerg@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Sean Wang <sean.wang@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>