net/mrvl: document policer/scheduler/rate limiter usage
net/mrvl: document policer/scheduler/rate limiter usage

Add documentation and example for ingress policer, egress scheduler
and egress rate limiter.

Signed-off-by: Natalie Samsonov <334157704ab7e2b8e1b2652d747d1fd920233923@marvell.com>
Signed-off-by: Tomasz Duszynski <389c907effde06d7d3e3fb2cf2ccfaf9dc5af62a@semihalf.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk