mtl: build all supporting code as LLEXT modules

Enable CONFIG_LIBRARY_DEFAULT_MODULAR for MTL to build all supporting
code as LLEXT modules.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

app/boards/intel_adsp_ace15_mtpm.conf

@@ -85,6 +85,7 @@ CONFIG_MEMORY_WIN_2_SIZE=12288
 CONFIG_LLEXT=y
 CONFIG_LLEXT_STORAGE_WRITABLE=y
 CONFIG_MODULES=y
+CONFIG_LIBRARY_DEFAULT_MODULAR=y
 
 # Temporary disabled options
 CONFIG_TRACE=n