net: dsa: microchip: move struct mib_names to ksz_chip_data

The ksz88xx family has one set of mib_names. The ksz87xx, ksz9477,
LAN937x based switches has one set of mib_names. In order to remove
redundant declaration, moved the struct mib_names to ksz_chip_data
structure.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>