config: apalis-imx8: Enable FEC TXC delay

config: apalis-imx8: Enable FEC TXC delay

define FEC_ENET_ENABLE_TXC_DELAY to enable the delay on TXC line on
the MAC. This has to be done in order to meet RGMII specs.
According to RGMII specs the clock should get delayed so the edges of
the clock are preferrably in the middle of the edges of data-lines so
they can be sampled properly.
Our PHY expects the MAC to delay TXC line, as it is also written
in the spec. This patch makes sure the TXC delay on the FEC is enabled

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>