Pass TFM_LVL macro to linker files

With this, single linker file can support different TFM security levels.

Author: ccli8

tools/toolchains/mbed_toolchain.py

@@ -918,6 +918,7 @@ def add_regions(self):
             pass
 
     STACK_PARAM = "target.boot-stack-size"
+    TFM_LVL_PARAM = "tfm.level"
 
     def add_linker_defines(self):
         params, _ = self.config_data
@@ -930,6 +931,15 @@ def add_linker_defines(self):
             self.ld.append(define_string)
             self.flags["ld"].append(define_string)
 
+        # Pass TFM_LVL to linker files, so single linker file can support different TFM security levels.
+        if self.TFM_LVL_PARAM in params:
+            define_string = self.make_ld_define(
+                "TFM_LVL",
+                params[self.TFM_LVL_PARAM].value
+            )
+            self.ld.append(define_string)
+            self.flags["ld"].append(define_string)
+
         if self.target.is_PSA_secure_target:
             for flag, param in [
                 ("MBED_PUBLIC_RAM_START", "target.public-ram-start"),