cmake: zephyr-package: add message mode

Explicitly set the <mode> value to the message printed when including
zephyr modules. The documentation is added to explain why it is
output to stderr, as this has been been subject of multiple PR's
(zephyrproject-rtos#31365,zephyrproject-rtos#43009).

Signed-off-by: Jordan Yates <[email protected]>

share/zephyr-package/cmake/ZephyrConfig.cmake

@@ -43,11 +43,14 @@ macro(include_boilerplate location)
 
   if(NOT NO_BOILERPLATE)
     list(LENGTH Zephyr_FIND_COMPONENTS components_length)
+    # The module messages are intentionally higher than STATUS to avoid the -- prefix
+    # and make them more visible to users. This does result in them being output
+    # to stderr, but that is an implementation detail of cmake.
     if(components_length EQUAL 0)
-      message("Loading Zephyr default modules (${location}).")
+      message(NOTICE "Loading Zephyr default modules (${location}).")
       include(zephyr_default NO_POLICY_SCOPE)
     else()
-      message("Loading Zephyr module(s) (${location}): ${Zephyr_FIND_COMPONENTS}")
+      message(NOTICE "Loading Zephyr module(s) (${location}): ${Zephyr_FIND_COMPONENTS}")
       foreach(component ${Zephyr_FIND_COMPONENTS})
         if(${component} MATCHES "^\([^:]*\):\(.*\)$")
           string(REPLACE "," ";" SUB_COMPONENTS ${CMAKE_MATCH_2})