net: mvpp2: add driver dependency to NET_DSA

commit 8e264165f085c215115a0e74f52f3342710eaaa4 from
git@git.assembla.com:cavium/WindRiver.linux.git

Since driver has dsa notifier callbacks

Change-Id: Icc8a7911dfe2d599c2a4126bf145b9043e7b2c85
Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/55377
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>