imx: ventana: enable dm support for PCI and FEC ethernet

Enable driver model support for FEC ethernet which allows us to remove
the iomux and board_eth_init function. Replace the toggling of the ethernet
phy reset with dt configuration.

Enable driver model support for PCI which allows us to remove the
eth1000_initialize() call. Additionally enable PCI_INIT_R to scan for
PCI devices on init such as the e1000 that is present on the GW552x.

Convert board_pci_fixup to use dm callback and remove pcidisable env
variable which is not supported for DM_PCI and thus leave PCI always
enabled during init.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>