arm64: dts: allwinner: a64: Pine64 Plus: Fix ethernet node

According to board schematic, PHY provides both, RX and TX delays.
However, according to "fix" Realtek provided for this board, only TX
delay should be provided by PHY.
Tests show that both variants work but TX only PHY delay works
slightly better.

Update ethernet node to reflect the fact that PHY provides TX delay.

Fixes: 94f44288 ("arm64: dts: allwinner: A64: Restore EMAC changes")
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201022211301.3548422-1-jernej.skrabec@siol.net