Added Python interface for Arm Ethos-U NPU driver library.

Python `ethosu_driver` could be built as part of Arm Ethos-U Linux
driver library CMake flow.

See driver_library/python/README.md for more details.

Change-Id: I177a890add5c13df9a839f4f43621f972afe5ab1
Signed-off-by: Kshitij Sisodia <kshitij.sisodia@arm.com>