imx6: icorem6: Add ENET support

imx6: icorem6: Add ENET support

Add enet support for engicam icorem6 qdl starter kit.
- Add pinmux settings
- Add board_eth_init

TFTP log:
--------
Net:   FEC [PRIME]
Hit any key to stop autoboot:  0
icorem6qdl> tftpboot {fdt_addr} imx6dl-icore.dtb
Using FEC device
TFTP from server 192.168.2.96; our IP address is 192.168.2.75
Filename 'imx6dl-icore.dtb'.
Load address: 0x0
Loading: ######
         1.3 MiB/s
done
Bytes transferred = 28976 (7130 hex)
CACHE: Misaligned operation at range [00000000, 00007130]
icorem6qdl>

Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>