mv643xx_eth: Move ethernet register definitions into private header

Move the mv643xx's ethernet-related register definitions from
include/linux/mv643xx.h into drivers/net/mv643xx_eth.h, since
they aren't of any use outside the ethernet driver.
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Tzachi Perelstein <tzachi@marvell.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>