secure_storage: its: transform: improve expandability

Instead of checking whether a custom implementation is present, check
whether the AEAD one is used.
This allows downstream users to expand the implementation choice with
more options.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>

subsys/secure_storage/CMakeLists.txt

@@ -31,9 +31,13 @@ if(CONFIG_SECURE_STORAGE_PS_IMPLEMENTATION_CUSTOM)
   make_available(ps.h)
 endif()
 
-if(CONFIG_SECURE_STORAGE_ITS_TRANSFORM_IMPLEMENTATION_CUSTOM)
-  make_available(its/transform.h)
-endif()
+if(CONFIG_SECURE_STORAGE_ITS_TRANSFORM_MODULE)
+
+  if(NOT CONFIG_SECURE_STORAGE_ITS_TRANSFORM_IMPLEMENTATION_AEAD)
+    make_available(its/transform.h)
+  endif()
+
+endif() # CONFIG_SECURE_STORAGE_ITS_TRANSFORM_MODULE
 
 if(CONFIG_SECURE_STORAGE_ITS_STORE_IMPLEMENTATION_CUSTOM)
   make_available(its/store.h)