mv643xx_eth: Remove MV643XX_ETH_ register prefix

Now that all register address and bit defines are in private
namespace (drivers/net/mv643xx_eth.h), we can safely remove the
MV643XX_ETH_ prefix to conserve horizontal space.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Tzachi Perelstein <tzachi@marvell.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>