stm32f4: need floating printf for libscpi

The SCPI_NumberToStr calls use snprintf, with floating point, so for
newlib-nano, need to use this extra flag to pull in floating point printf
support.
Support loading arbitrary data into waveform memory

No way of outputting it yet, but you can load/dump custom data

Only tested on the native tcp server
Support user defined function output

Still lots of bugs in large USB transfers...