mv643xx_eth: Merge drivers/net/mv643xx_eth.h into mv643xx_eth.c

Since drivers/net/mv643xx_eth.c is the only user of
drivers/net/mv643xx_eth.h, there's not much use in having the header
file as a separate file, so merge the header into the driver.
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>