Free Heap information for STM32 NUCLEO F411 board not implemented yet

[dniklaus]

Error description

When the wiring-skeleton firmware is built for running on an STM32 NUCLE F411 board (that is claimed to be supported) the free heap indication trace output always prints zero.

Steps to reproduce

1. Attach a terminal to the serial USB and enter the following CLI command:
   dbg tr heap lvl set debug
2. wait 5 seconds until the first trace output will be written:
   10000 - heap: 0 bytes free