net: lan966x: Add support for offloading pcp table

Add support for offloading pcp app entries. Lan966x has 8 priority
queues per port and for each priority it also has a drop precedence.

Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Piotr Raczynski <piotr.raczynski@intel.com>
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>