powerpc/5200: Stop using device_type and port-number properties

There is no reason for the PSC UART driver or the Ethernet driver
to require a device_type property.  The compatible value is sufficient
to uniquely identify the device.  Remove it from the driver.

The whole 'port-number' scheme for assigning numbers to PSC uarts was
always rather half baked and just adds complexity.  Remove it from the
driver.  After this patch is applied, PSC UART numbers are simply
assigned from the order they are found in the device tree (just like
all the other devices).  Userspace can query sysfs to determine what
ttyPSC number is assigned to each PSC instance.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Reviewed-by: Wolfram Sang <w.sang@pengutronix.de>