rawdev: add telemetry callbacks

rawdev: add telemetry callbacks

The rawdev library now registers commands with telemetry, and
implements the corresponding callback functions. These allow a list of
rawdev devices and xstats for a rawdev port to be queried.

An example usage, with ioat rawdev driver instances, is shown below:

Connecting to /var/run/dpdk/rte/dpdk_telemetry.v2
{"version": "DPDK 20.05.0-rc0", "pid": 65777, "max_output_len": 16384}
--> /
{"/": ["/", "/ethdev/link_status", "/ethdev/list", "/ethdev/xstats", \
    "/help", "/info", "/rawdev/list", "/rawdev/xstats"]}
--> /rawdev/list
{"/rawdev/list": [0, 1, 2, 3, 4, 5]}
--> /rawdev/xstats,0
{"/rawdev/xstats": {"failed_enqueues": 0, "successful_enqueues": 0, \
    "copies_started": 0, "copies_completed": 0}}

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Ciara Power <ciara.power@intel.com>
Reviewed-by: Keith Wiles <keith.wiles@intel.com>