ARM: dts: pfla02: add ksz9031 clock skew values

The pfla02 SoM has a Micrel KSZ9031RNX ethernet phy connected to the FEC,
which needs RX and TX clock skew settings to compensate for differences
in line length. The skew values are taken from barebox commit
4c65c20f1071 ("ARM: pfla02: Set new ethernet phy tx timings"), which
is based on patches originally provided by Phytec:

    TX_CLK line is approx. 54mm longer than other TX lines which adds
    a delay of 0.36ns. RGMII need a delay of min. 1.0ns. This mean we
    have to add a delay of 0.64ns. We choose 0.78 to have a little gap.
    This can be done by setting GTX pad skew value to 11100
    Also add a delay for the RX delay lines, needed for the Duallite
    variant.  => Set register 2.8 (RGMII Clock Pad Skew) to 0x039F.

Cc: Christian Hemp <c.hemp@phytec.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>