mlxsw: reg: Add the Switch Port Acceptable Frame Types register

When VLAN filtering is enabled on a bridge and PVID is deleted from a
bridge port, then untagged frames are not allowed to ingress into the
bridge from this port.

Add the Switch Port Acceptable Frame Types (SPAFT) register, which
configures the frame admittance of the port.

Fixes: 56ade8fe

 ("mlxsw: spectrum: Add initial support for Spectrum ASIC")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>