ARM: dts: armada-388-clearfog: Utilize new DSA binding

Utilize the new DSA binding, introduced with commit 8c5ad1d6

 ("net:
dsa: Document new binding"). The legacy binding node is kept included, but is
marked disabled.

Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>