rawdev: allow getting info for unknown device

rawdev: allow getting info for unknown device

To call the rte_rawdev_info_get() function, the user currently has to know
the underlying type of the device in order to pass an appropriate structure
or buffer as the dev_private pointer in the info structure. By allowing a
NULL value for this field, we can skip getting the device-specific info and
just return the generic info - including the device name and driver, which
can be used to determine the device type - to the user.

This ensures that basic info can be get for all rawdevs, without knowing
the type, and even if the info driver API call has not been implemented for
the device.

Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>