mv643xx_eth: shorten shared platform driver name

Change the MV643XX_ETH_SHARED_NAME platform driver name to something
shorter than 19 characters, so that we can register multiple (otherwise
we end up with sysfs conflicts since all instances will map to
"mv643xx_eth_shared." as there is a 20-char sysfs file name limit.)

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>