Update zephyr side to handle hal_nxp using cmake-ext/kconfig-ext. This
allows for having zephyr specific integration code live with the zephyr
source tree.
For now on the cmake side we just use add_subdirectory() of the hal_nxp
repo so the integration is effectively transparent.
For Kconfig we add a place holder Kconfig file since the hal_nxp repo
doesn't have any Kconfig files in it currently.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
