ARM: dts: vf610-zii-dev: add EEPROM entry to Rev C

The ZII Dev Rev C board has EEPROMs hanging the 88E6390 Ethernet switch
chips. Add an "eeprom-length" property to allow access from ethtool.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>