mv643xx_eth: introduce per-port register area pointer

The mv643xx_eth driver uses the rdl()/wrl() macros to read and
write hardware registers.  Per-port registers are accessed in the
following way:

	#define PORT_STATUS(p)			(0x0444 + ((p) << 10))

	[...]

	static inline u32 rdl(struct mv643xx_eth_private *mp, int offset)
	{
		return readl(mp->shared->base + offset);
	}

	[...]

	port_status = rdl(mp, PORT_STATUS(mp->port_num));

By giving the per-port 'struct mv643xx_eth_private' its own
'void __iomem *base' pointer that points to the per-port register
area, we can get rid of both the double indirection and the << 10
that is done for every per-port register access -- this patch does
that.
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>