ARM: imx: imx8mm: Add missing clock entries for FEC clock

ARM: imx: imx8mm: Add missing clock entries for FEC clock

All the FEC ethernet clock entries for iMX8MM are missing, while they
are already present on iMX8MQ. Fill in the nodes on iMX8MM, as the FEC
ethernet gets bogus clock information otherwise which makes ethernet
inoperable.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>