This provides a better error message when building with CMake and
forgetting ZEPHYR_BASE or not registering Zephyr in the CMake package
registry. See parent commit for more details (split from parent for
better readability).
Signed-off-by: Marc Herbert <marc.herbert@intel.com>
The difference between "blinky" and "blink_led" is not clear.
This rename makes it more obvious that "blinky_pwm", well,
blinks an LED using PWM.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>