Merge pull request ARMmbed#398 from 23chrischen/master

Added INITIAL_SP for F411

Author: bogdanm

libraries/rtos/rtx/RTX_CM_lib.h

@@ -253,6 +253,9 @@ osThreadDef_t os_thread_def_main = {(os_pthread)main, osPriorityNormal, 0, NULL}
 #elif defined(TARGET_NRF51822)
 #define INITIAL_SP            (0x20004000UL)
 
+#elif defined(TARGET_STM32F411RE)
+#define INITIAL_SP            (0x20020000UL)
+
 #else
 #error "no target defined"