ARM: mvebu: Reenable DSA in mvebu_v5_defconfig

DSA now depends on switchdev. Enable it, and re-enable DSA and its
drivers, which were removed when mvebu_v5_defconfig was regenerated.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>