picoc/platform.h: Enable USE_MALLOC_HEAP macro.
lm3s/platform.c: Add support for PicoC.
lm3s/lm3s_pio.c: Add conditional compilation for PicoC.

TODO: lm3s_pio functions for PicoC.
lm3s/platform_conf.h: Extend config file to include initial
support for PicoC.

Alcor6L-PicoC can now run on LM3S* (tested on LM3S8962).