examples/l3fwd-power: add telemetry mode

examples/l3fwd-power: add telemetry mode

Add new telemetry mode support for l3fwd-power.
This is a standalone mode, in this mode l3fwd-power
does simple l3fwding along with calculating
empty polls, full polls, and busy percentage for
each forwarding core. The aggregation of these
values of all cores is reported as application
level telemetry to metric library for every 500ms from the
master core.

The busy percentage is calculated by recording the poll_count
and when the count reaches a defined value the total
cycles it took is measured and compared with minimum and maximum
reference cycles and busy rate is set according to either 0% or
50% or 100%.

Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>