imx: ventana: default pci to disabled

The IMX6 PCIe host controller does not have a proper reset and as such there
are several issues that can arise if PCI is enabled in the bootloader follwed
by Linux trying to re-configure LTSSM and/or toggling PERST# to the devices.

For now, the best approach seems to default to disabling PCI by defaulting
pciedisable=1. This can be overridden by the user if they need PCI in the
bootloader, for example:
 - GW552x needing ethernet access in bootloader
 - GW16082 expansion board needing a device-tree fixup for irq mapping
Signed-off-by: NTim Harvey <tharvey@gateworks.com>

include/configs/gw_ventana.h

@@ -274,6 +274,7 @@
 	"dio0:mode=gpio;dio1:mode=gpio;dio2:mode=gpio;dio3:mode=gpio\0" \
 
 #define CONFIG_EXTRA_ENV_SETTINGS_COMMON \
+	"pcidisable=1\0" \
 	"usb_pgood_delay=2000\0" \
 	"console=ttymxc1\0" \
 	"bootdevs=usb mmc sata flash\0" \