[POWERPC] mv643xx_eth: Prepare to support multiple silicon blocks

The mv643xx_eth driver is being modified to support multiple instances
of the ethernet silicon block on the same platform.  Each block contains
a single register bank containing the registers for up to three ports
interleaved within that bank.  This patch updates the PowerPC OF to
platform_device glue code to support multiple silicon blocks, each
with up to three ethernet ports.  The main difference is that we now
allow multiple mv64x60_shared platform_devices to be registered and
we provide each port platform_device with a pointer to its associated
shared platform_device.  The pointer will not be used until the
mv643xx_eth driver changes are committed.

Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Acked-by: Mark Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>