net: dsa: microchip: add KSZ9477 I2C driver

Add KSZ9477 I2C driver support.  The code ksz9477.c and ksz_common.c are
used together to generate the I2C driver.

Signed-off-by: Tristram Ha <Tristram.Ha@microchip.com>
[george.mccollister@gmail.com: bring up to date, use ksz_common regmap macros]
Signed-off-by: George McCollister <george.mccollister@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>