[nrf fromtree] cmake: update zephyr_file to use cmake_path()

Since the introduction of zephyr_file() then the minimum required CMake
version has become 3.20.
Update zephyr_file() to use cmake_path insteasd of set().
This allows us to normalize the path and thereby also remove duplicates
in the list as paths are normalized.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
(cherry picked from commit 8b3d4c6)

cmake/modules/extensions.cmake

@@ -2609,11 +2609,11 @@ Please provide one of following: APPLICATION_ROOT, CONF_FILES")
       # `set(<var> CACHE)`, so let's update current scope variable to absolute
       # path from  `APPLICATION_SOURCE_DIR`.
       if(NOT IS_ABSOLUTE ${path})
-        set(abs_path ${APPLICATION_SOURCE_DIR}/${path})
         list(FIND ${ZFILE_APPLICATION_ROOT} ${path} index)
+	cmake_path(ABSOLUTE_PATH path BASE_DIRECTORY ${APPLICATION_SOURCE_DIR} NORMALIZE)
         if(NOT ${index} LESS 0)
           list(REMOVE_AT ${ZFILE_APPLICATION_ROOT} ${index})
-          list(INSERT ${ZFILE_APPLICATION_ROOT} ${index} ${abs_path})
+          list(INSERT ${ZFILE_APPLICATION_ROOT} ${index} ${path})
         endif()
       endif()
     endforeach()
@@ -2630,6 +2630,7 @@ Relative paths are only allowed with `-D${ARGV1}=<path>`")
       endif()
     endforeach()
 
+    list(REMOVE_DUPLICATES ZFILE_APPLICATION_ROOT)
     # This updates the provided argument in parent scope (callers scope)
     set(${ZFILE_APPLICATION_ROOT} ${${ZFILE_APPLICATION_ROOT}} PARENT_SCOPE)
   endif()