build: clean up the mess of ifdefs from platform into a scons-configured hal

build-hal.py

@@ -0,0 +1,9 @@
+Import("env")
+board = env.get("BOARD_MCU")
+frameworks = env.get("PIOFRAMEWORK")
+
+print(f"HAL configuration:")
+for framework in frameworks:
+    env.Append(SRC_FILTER=[f"+<platform/{framework}/{board}/*>"])
+    env.Append(SRC_FILTER=[f"+<platform/{framework}/*.cpp>"])
+    print(f"- platform/{framework}{board}")