Merge pull request #4958 from soramame21/master

Add bootloader support for DISCO_L476VG

Author: 0xc0170

targets/targets.json

@@ -1594,7 +1594,8 @@
         "macros_add": ["USBHOST_OTHER"],
         "device_has_add": ["ANALOGOUT", "CAN", "LOWPOWERTIMER", "SERIAL_FC", "TRNG", "FLASH"],
         "release_versions": ["2", "5"],
-        "device_name": "STM32L476VG"
+        "device_name": "STM32L476VG",
+        "bootloader_supported": true
     },
     "MTS_MDOT_F405RG": {
         "inherits": ["FAMILY_STM32"],