net: microchip: sparx5: add support for Service Dual Leacky Buckets

Add support for Service Dual Leacky Buckets (SDLB), used to implement
PSFP flow-meters. Buckets are linked together in a leak chain of a leak
group. Leak groups a preconfigured to serve buckets within a certain
rate interval.

Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>