net: mscc: ocelot: move NPI port configuration to DSA

Remove the ocelot_configure_cpu() function, which was in fact bringing
up 2 ports: the CPU port module, which both switchdev and DSA have, and
the NPI port, which only DSA has.

The (non-Ethernet) CPU port module is at a fixed index in the analyzer,
whereas the NPI port is selected through the "ethernet" property in the
device tree.

Therefore, the function to set up an NPI port is DSA-specific, so we
move it there, simplifying the ocelot switch library a little bit.

Cc: Horatiu Vultur <horatiu.vultur@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: UNGLinuxDriver <UNGLinuxDriver@microchip.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>