mvebu: cortexa9: disable devices using broken mv88e6176 switch

mvebu: cortexa9: disable devices using broken mv88e6176 switch

Several users have reported, that devices using mv88e6176 switch are
seriously broken, basically turning that switch into a hub. Until fixed
those devices should be disabled.

I've used TOH with "Switch 88E6176" filter, which provided me with the
following list of likely affected devices:

 * Linksys WRT1200AC v1/v2, WRT1900AC v1/v2
 * SolidRun ClearFog Pro
 * Turris Omnia

That device list more or less corresponds with the list of devices
mentioned in the linked bug reports.

References: https://github.com/openwrt/openwrt/issues/11077
Signed-off-by: Petr Štetiar <ynezz@true.cz>