net: dsa: mv88e6xxx: add irl_init_all op

Some Marvell chips have an Ingress Rate Limit unit. But the command
values slightly differs between models: 88E6352 use 3-bit for operations
while 88E6390 use different 2-bit operations.

This commit kills the IRL flags in favor of a new operation implementing
the "Init all resources to the initial state" operation.

This fixes the operation of 88E6390 family where 0x1000 means Read the
selected resource 0, register 0 on port 16, instead of init all.

A mv88e6xxx_irl_setup helper is added to wrap the operation call.

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