net/mvpp2: change default policer configuration

net/mvpp2: change default policer configuration

Change QoS configuration file syntax for port's default policer
setup.

Since default policer configuration is performed before
any other policer configuration we can pick a default id.

This simplifies default policer configuration since user
no longer has to choose ids from range [0, PP2_CLS_PLCR_NUM].

Explicitly document values for rate_limit_enable field.

Signed-off-by: Tomasz Duszynski <tdu@semihalf.com>
Signed-off-by: Natalie Samsonov <nsamsono@marvell.com>
Reviewed-by: Liron Himi <lironh@marvell.com>