MLECO-2948: Minor refactoring for platform modules.

Reducing dependency on cmsis-device sources as these will
be removed under MLECO-2944. Also, starting to refactor
to allow HAL to drop NPU and TA init routines - this will
happen in future CRs.

Added platform driver for native, and subsequent patches
will attempt to get rid of the HAL "profile" specific
sources and allow platform stub implementations at a level
below HAL. This will allow platforms drivers to only
override the range of functions that they actually want to
implement and will fall back on stubs for the rest. In this
CR only "utils" have been removed.

Change-Id: I09b4a28e20847a07a956c818c6f47c74aab89063
diff --git a/source/hal/platform/mps3/source/device_mps3.c b/source/hal/platform/mps3/source/device_mps3.c
index fa57c2e..de715fb 100644
--- a/source/hal/platform/mps3/source/device_mps3.c
+++ b/source/hal/platform/mps3/source/device_mps3.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -21,11 +21,9 @@
 
 #include <inttypes.h>
 
-extern uint32_t GetSystemCoreClock(void);
-
 uint32_t GetMPS3CoreClock(void)
 {
-    const uint32_t default_clock = GetSystemCoreClock();
+    const uint32_t default_clock = 32000000 /* 32 MHz clock */;
     static int warned_once = 0;
     if (0 != MPS3_SCC->CFG_ACLK) {
         if (default_clock != MPS3_SCC->CFG_ACLK) {