net: mvpp2: enable building on 64-bit platforms

The mvpp2 is going to be extended to support the Marvell Armada 7K/8K
platform, which is ARM64. As a preparation to this work, this commit
enables building the mvpp2 driver on ARM64, by:

 - Adjusting the Kconfig dependency

 - Fixing the types used in the driver so that they are 32/64-bits
   compliant. We use dma_addr_t for DMA addresses, and unsigned long
   for virtual addresses.

It is worth mentioning that after this commit, the driver is for now
still only used on 32-bits platforms, and will only work on 32-bits
platforms.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>