mlxsw: reg: Add Policy-Engine General Configuration Register

The PGCR register configures general Policy-Engine settings.

Specifically, we are going to use it in order to set the default action
base pointer, which determines where the default action (when there is
no hit) is located for each region.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>