net: mvpp2: use the same buffer pool for all ports

This patch configures the buffer manager long pool for all ports part of
the same CP. Long pool separation between ports is redundant since there
are no performance improvement when different pools are used.

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
[Antoine: cosmetic cleanup, commit message]
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>