mvpp2: use page_pool allocator

Use the page_pool API for memory management.
This is a prerequisite for native XDP support.

Tested-by: Sven Auhagen <sven.auhagen@voleatech.de>
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>