net: dsa: microchip: generic access to ksz9477 static and reserved table

The ksz9477 and lan937x has few difference in the static and reserved
table register 0x041C. For the ksz9477 if the bit 0 is 1 - read
operation and 0 - write operation. But for lan937x bit 1:0 used for
selecting the read/write operation, 01 - write and 10 - read.
To use ksz9477 mdb add/del and enable_stp_addr for the lan937x, masks &
shifts are introduced for ksz9477 & lan937x in ksz_common.c. Then
updated the function with masks & shifts based on the switch instead of
hard coding it.

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