net: dsa: mv88e6xxx: distinguish Global 2 Rsvd2CPU

The 88E6185 family only has one 16-bit register to mark the 16 802.1D
reserved multicast addresses in the range of 01:80:C2:00:00:0x as MGMT.

The 88E6352 family also has one 16-bit register to mark the 16 GARP
reserved multicast addresses in the range of 01:80:C2:00:00:2x as MGMT.

Split the existing mv88e6095 prefixed mgmt_rsvd2cpu operation into two
distinct mv88e6185 and mv88e6352 prefixed operations, and wrap its call
into a mv88e6xxx_rsvd2cpu_setup helper.

This allows us to also get rid of the MV88E6XXX_CAP_G2_MGMT_EN_* flags.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>