arm64: dts: amlogic: Add the Ethernet "timing-adjustment" clock

Add the "timing-adjustment" clock now that we know how it is connected
to the PRG_ETHERNET registers. It is used internally to generate the
RGMII RX delay on the MAC side (if needed).

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20200620162347.26159-1-martin.blumenstingl@googlemail.com