Replaces the special heap command approach of the lpc_common module with a more general heap command approach. Module lpc_common was already removed with PR #2118. PR #2118 integrated cpu/lpc_common code in cpu/lpc2387. With PR #3530 special heap handling for cpu/lpc2387 was replaced by newlib memory management which uses _sbrk_r to allocate chunks from the heap. _sbrk_r uses _sheap and _eheap symbols that are defined in lpc2387.ld and can be used together with mallinfo function for heap statistics.