rockchip: Enable ETH address randomization for the rock2

This commit enables ethernet MAC address randomization on the rock2. It
removes the error at startup 'ethernet@ff290000 address not set'.

Signed-off-by: Romain Perier <romain.perier@collabora.com>

configs/rock2_defconfig

@@ -32,6 +32,7 @@ CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_SPL_OF_CONTROL=y
 CONFIG_OF_SPL_REMOVE_PROPS="pinctrl-0 pinctrl-names clock-names interrupt-parent"
+CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_REGMAP=y
 CONFIG_SPL_REGMAP=y
 CONFIG_SYSCON=y