Updates the Zephyr port build instructions. The CI is updated to use
Zephyr docker image 0.27.4, SDK 0.17.0 and the latest Zephyr release
tag.
Tested on max32690fthr and frdm_k64f.
Signed-off-by: Maureen Helm <maureen.helm@analog.com>
Signed-off-by: Detlev Zundel <dzu@member.fsf.org>