Add STM_F439 MTB

Author: Ashok Rao

src/mbed_os_tools/detect/platform_database.py

@@ -105,6 +105,7 @@
         u"0465": u"MTB_LAIRD_BL654",
         u"0466": u"MTB_MURATA_WSM_BL241",
         u"0468": u"MTB_STM_L475",
+        u"0469": u"MTB_STM32_F439",
         u"0472": u"MTB_ACONNO_ACN52832",
         u"0500": u"SPANSION_PLACEHOLDER",
         u"0505": u"SPANSION_PLACEHOLDER",