Fix hard fault due to uninitialized MPU BSS section

In the MPU protected BSS section, there is a flag indicating whether static instance has been created or not.
The flag is not cleared and during a power interruption, the flag sometimes has a random value.
This caused the SafeSupervisor static object to have random incorrect values due to missing constructor call,
which leads to unintended behaviour, e.g. false positive safety checks.

The solution is to zero out MPU protected BSS section.

Change-Id: I5de341b0fd14a64b0c5b21a8b82a1ce30c6cfba8

Author: nemadhu

executables/referenceApp/platforms/s32k148evb/main/src/bsp/startUp.S

@@ -431,6 +431,22 @@ Reset_Handler:
     bge .LC2
 .LC3:
 
+/*
+ * Zero out the MPU protected BSS section
+ */
+    ldr r1, =__MPU_BSS_START
+    ldr r2, =__MPU_BSS_END
+
+    subs    r2, r1
+    ble .LC7
+
+    movs    r0, 0
+.LC6:
+    str r0, [r1, r2]
+    subs    r2, 4
+    bge .LC6
+.LC7:
+
 #ifndef __START
 #define __START _start
 #endif