OLIMEX_STM32E407_F407ZG: bootloader support

This commit modifies the Vector Table Offset Register in the startup
file, so it uses address coming from the user application instead of a
fixed one pointing to the bootloader. This change has been already
proposed for another STM32F4 board [1] to fix bootloader issues.

1. #1666 (comment)

Author: msuminsk

targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F407xG/TARGET_OLIMEX_STM32E407_F407ZG/system_clock.c

@@ -31,6 +31,7 @@
 
 #include "stm32f4xx.h"
 #include "mbed_error.h"
+#include "nvic_addr.h"
 
 /*!< Uncomment the following line if you need to relocate your vector Table in
      Internal SRAM. */
@@ -94,7 +95,7 @@ void SystemInit(void)
 #ifdef VECT_TAB_SRAM
     SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM */
 #else
-    SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH */
+    SCB->VTOR = NVIC_FLASH_VECTOR_ADDRESS; /* Vector Table Relocation in Internal FLASH */
 #endif
 
 }

targets/targets.json

@@ -4092,7 +4092,8 @@
             "USBDEVICE"
         ],
         "release_versions": ["5"],
-        "device_name": "STM32F407ZG"
+        "device_name": "STM32F407ZG",
+        "bootloader_supported": true
     },
     "DISCO_F429ZI": {
         "inherits": ["FAMILY_STM32"],