dt-bindings: net: dwmac-meson: Document the "timing-adjustment" clock
The PRG_ETHERNET registers can add an RX delay in RGMII mode. This
requires an internal re-timing circuit whose input clock is called
"timing adjustment clock". Document this clock input so the clock can be
enabled as needed.
Reviewed-by: Andrew Lunn <andrew@lunn.ch> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> Signed-off-by: David S. Miller <davem@davemloft.net>