ext: mcux: Add a script to import new versions of mcux

NXP periodically releases new versions of the MCUXpresso SDK (mcux).
Automate the process of importing mcux into zephyr with a python script.

Example usage:

$ import_mcux_sdk.py -f SDK_2.3.0_EVK-MIMXRT1050.tar.gz

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>