ARM: dts: imx6ul: segin: Reduce eth drive strength

Reduce the drive strength for the MDC, MDIO and TX pins of FEC1 and FEC2
on the phyBOARD-Segin to improve signal quality and EMC. Also disable
internal pull-ups on the MDC and MDIO pins.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>