RVDS/Keil weak linkage for vPortSetupTimerInterrupt() -- CM4F, CM3

Test steps are documented in this PR https://github.com/aws/amazon-freertos/pull/1141.

FreeRTOS/Source/portable/RVDS/ARM_CM3/port.c

@@ -1,4 +1,4 @@
-/*
+-/*
  * FreeRTOS Kernel V10.2.1
  * Copyright (C) 2019 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
  *
@@ -603,7 +603,7 @@ void xPortSysTickHandler( void )
  */
 #if( configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0 )
 
-	void vPortSetupTimerInterrupt( void )
+	__weak void vPortSetupTimerInterrupt( void )
 	{
 		/* Calculate the constants required to configure the tick interrupt. */
 		#if( configUSE_TICKLESS_IDLE == 1 )

FreeRTOS/Source/portable/RVDS/ARM_CM4F/port.c

@@ -693,7 +693,7 @@ void xPortSysTickHandler( void )
  */
 #if( configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0 )
 
-	void vPortSetupTimerInterrupt( void )
+	__weak void vPortSetupTimerInterrupt( void )
 	{
 		/* Calculate the constants required to configure the tick interrupt. */
 		#if( configUSE_TICKLESS_IDLE == 1 )