net: ti: icssg-prueth: Add helper functions to configure FDB

Introduce helper functions to configure firmware FDB tables, VLAN tables
and Port VLAN ID settings to aid adding Switch mode support.

Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>