eal: add telemetry callbacks

eal: add telemetry callbacks

EAL now registers commands to provide some basic info from EAL.

Example:
Connecting to /var/run/dpdk/rte/dpdk_telemetry.v2
{"version": "DPDK 20.05.0-rc0", "pid": 72662, "max_output_len": 16384}
--> /
{"/": ["/", "/eal/app_params", "/eal/params", "/ethdev/link_status", \
    "/ethdev/list", "/ethdev/xstats", "/help", "/info", "/rawdev/list", \
    "/rawdev/xstats"]}
--> /eal/app_params
{"/eal/app_params": ["-i"]}
--> /eal/params
{"/eal/params": ["./app/dpdk-testpmd"]}

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>