The internal Ethernet switch suffers from erratum A-050484 ("Ethernet
flow control not functional on L2 switch NPI port when XFH is used").
XFH stands for "Extraction Frame Header" - which basically means the
default "ocelot" DSA tagging protocol.

However, the switch supports one other tagging protocol - "ocelot-8021q",
and this is not subject to the erratum above. So describe the hardware
ability to pass PAUSE frames in the device tree, and let the driver
figure out whether it should use flow control on the CPU port or not,
depending on whether the "ocelot" or "ocelot-8021q" tagging protocol is
being used.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>