configs: pico-imx6: convert ethernet function to DM_ETH
Before enable _DM_ETH:
Net: FEC [PRIME]
After enable DM_ETH:
Net: eth0: ethernet@2188000
Here is the test commands:
=> dhcp
BOOTP broadcast 1
DHCP client bound to address 10.88.88.152 (146 ms)
*** ERROR: `serverip' not set
Cannot autoload with TFTPGET
=> ping 8.8.8.8
Using ethernet@2188000 device
host 8.8.8.8 is alive
Signed-off-by: Wig Cheng <wig.cheng@technexion.com>