net: mvpp2: Add remove function that is called before the OS is started

net: mvpp2: Add remove function that is called before the OS is started

This patch adds a remove function to the mvpp2 ethernet driver which is
called before the OS is started, doing:

- Allocate the used buffers back from the buffer manager
- Stop the BM activity

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Stefan Chulski <stefanc@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>