Platform: Add system reset hal function in SPM

Add tfm_spm_hal_system_reset() function which is used by SPM to reset
the system.
All platforms have the same implementation except for Musca-B1.

Change-Id: I1fe34d9026b9ec35bf981ea9fc6b5a92d391ed58
Signed-off-by: Edison Ai <edison.ai@arm.com>
diff --git a/platform/include/tfm_spm_hal.h b/platform/include/tfm_spm_hal.h
index 14a4a27..1bc2626 100644
--- a/platform/include/tfm_spm_hal.h
+++ b/platform/include/tfm_spm_hal.h
@@ -160,6 +160,11 @@
 enum tfm_plat_err_t tfm_spm_hal_system_reset_cfg(void);
 
 /**
+ * \brief System reset
+ */
+void tfm_spm_hal_system_reset(void);
+
+/**
  * \brief Configures all external interrupts to target the
  *        NS state, apart for the ones associated to secure
  *        peripherals (plus MPC and PPC)